SQL Complete Tutorial. All Topics Covered
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This document is a comprehensive SQL tutorial aimed at beginners, covering fundamental to advanced concepts of Structured Query Language (SQL) and Relational Database Management Systems (RDBMS). It includes information on SQL commands, data types, constraints, normalization, and the execution process of SQL commands, along with practical examples to help users understand key concepts. The tutorial also provides prerequisites for learning and resources to practice SQL online.
![Command Description
GRANT Gives a privilege to user
REVOKE Takes back privileges granted from user
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![Normalization guidelines are divided into normal forms; think of form as the format or the way a
database structure is laid out. The aim of normal forms is to organize the database structure so
that it complies with the rules of first normal form, then second normal form, and finally third
normal form.
It's your choice to take it further and go to fourth normal form, fifth normal form, and so on, but
generally speaking, third normal form is enough.
First Normal Form 1NF
Second Normal Form 2NF
Third Normal Form 3NF
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![SQL - PRIMARY KEYSQL - PRIMARY KEY
A primary key is a field in a table which uniquely identifies each row/record in a database table.
Primary keys must contain unique values. A primary key column cannot have NULL values.
A table can have only one primary key, which may consist of single or multiple fields. When
multiple fields are used as a primary key, they are called a composite key.
If a table has a primary key defined on any fields, then you can not have two records having the
same value of that fields.
Note: You would use these concepts while creating database tables.
Create Primary Key:
Here is the syntax to define ID attribute as a primary key in a CUSTOMERS table.
CREATE TABLE CUSTOMERS(
ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25) ,
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID)
);
To create a PRIMARY KEY constraint on the "ID" column when CUSTOMERS table already exists, use
the following SQL syntax:
ALTER TABLE CUSTOMER ADD PRIMARY KEY (ID);
NOTE: If you use the ALTER TABLE statement to add a primary key, the primary key columns must
already have been declared to not contain NULL values whenthetablewasfirstcreated.
For defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:
CREATE TABLE CUSTOMERS(
ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25) ,
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID, NAME)
);
To create a PRIMARY KEY constraint on the "ID" and "NAMES" columns when CUSTOMERS table
already exists, use the following SQL syntax:
ALTER TABLE CUSTOMERS
ADD CONSTRAINT PK_CUSTID PRIMARY KEY (ID, NAME);
Delete Primary Key:
You can clear the primary key constraints from the table, Use Syntax:
ALTER TABLE CUSTOMERS DROP PRIMARY KEY ;
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![SQL - FOREIGN KEYSQL - FOREIGN KEY
A foreign key is a key used to link two tables together. This is sometimes called a referencing key.
Foreign Key is a column or a combination of columns whose values match a Primary Key in a
different table.
The relationship between 2 tables matches the Primary Key in one of the tables with a
Foreign Key in the second table.
If a table has a primary key defined on any fields, then you can not have two records having the
same value of that fields.
Example:
Consider the structure of the two tables as follows:
CUSTOMERS table:
CREATE TABLE CUSTOMERS(
ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25) ,
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID)
);
ORDERS table:
CREATE TABLE ORDERS (
ID INT NOT NULL,
DATE DATETIME,
CUSTOMER_ID INT references CUSTOMERS(ID),
AMOUNT double,
PRIMARY KEY (ID)
);
If ORDERS table has already been created, and the foreign key has not yet been set, use the
syntax for specifying a foreign key by altering a table.
ALTER TABLE ORDERS
ADD FOREIGN KEY (Customer_ID) REFERENCES CUSTOMERS (ID);
DROP a FOREIGN KEY Constraint:
To drop a FOREIGN KEY constraint, use the following SQL:
ALTER TABLE ORDERS
DROP FOREIGN KEY;
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![MS Access comes with the professional edition of MS Office package. MS Access has easy-to-use
intuitive graphical interface.
1992 - Access version 1.0 was released.
1993 - Access 1.1 released to improve compatibility with inclusion the Access Basic
programming language.
The most significant transition was from Access 97 to Access 2000
2007 - Access 2007, a new database format was introduced ACCDB which supports complex
data types such as multi valued and attachment fields.
Features:
Users can create tables, queries, forms and reports and connect them together with macros.
The import and export of data to many formats including Excel, Outlook, ASCII, dBase,
Paradox, FoxPro, SQL Server, Oracle, ODBC, etc.
There is also the Jet Database format MDBorACCDBinAccess2007, which can contain the
application and data in one file. This makes it very convenient to distribute the entire
application to another user, who can run it in disconnected environments.
Microsoft Access offers parameterized queries. These queries and Access tables can be
referenced from other programs like VB6 and .NET through DAO or ADO.
The desktop editions of Microsoft SQL Server can be used with Access as an alternative to the
Jet Database Engine.
Microsoft Access is a file server-based database. Unlike client-server relational database
management systems RDBMS, Microsoft Access does not implement database triggers,
stored procedures, or transaction logging.
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![ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype};
SQL ALTER TABLE Statement Rename :
ALTER TABLE table_name RENAME TO new_table_name;
SQL INSERT INTO Statement:
INSERT INTO table_name( column1, column2....columnN)
VALUES ( value1, value2....valueN);
SQL UPDATE Statement:
UPDATE table_name
SET column1 = value1, column2 = value2....columnN=valueN
[ WHERE CONDITION ];
SQL DELETE Statement:
DELETE FROM table_name
WHERE {CONDITION};
SQL CREATE DATABASE Statement:
CREATE DATABASE database_name;
SQL DROP DATABASE Statement:
DROP DATABASE database_name;
SQL USE Statement:
USE database_name;
SQL COMMIT Statement:
COMMIT;
SQL ROLLBACK Statement:
ROLLBACK;
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![variable SQLServer2005only.
cursor Reference to a cursor object
table Stores a result set for later processing
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![UNIQUE The UNIQUE operator searches every row of a specified table for uniqueness
noduplicates.
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![SQL - EXPRESSIONSSQL - EXPRESSIONS
An expression is a combination of one or more values, operators, and SQL functions that evaluate
to a value.
SQL EXPRESSIONs are like formulas and they are written in query language. You can also use them
to query the database for specific set of data.
Syntax:
Consider the basic syntax of the SELECT statement as follows:
SELECT column1, column2, columnN
FROM table_name
WHERE [CONDITION|EXPRESSION];
There are different types of SQL expressions, which are mentioned below:
SQL - Boolean Expressions:
SQL Boolean Expressions fetch the data on the basis of matching single value. Following is the
syntax:
SELECT column1, column2, columnN
FROM table_name
WHERE SINGLE VALUE MATCHTING EXPRESSION;
Consider the CUSTOMERS table having the following records:
SQL> SELECT * FROM CUSTOMERS;
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
7 rows in set (0.00 sec)
Here is simple example showing usage of SQL Boolean Expressions:
SQL> SELECT * FROM CUSTOMERS WHERE SALARY = 10000;
+----+-------+-----+---------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+-------+-----+---------+----------+
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+-------+-----+---------+----------+
1 row in set (0.00 sec)
SQL - Numeric Expression:
This expression is used to perform any mathematical operation in any query. Following is the
syntax:
SELECT numerical_expression as OPERATION_NAME
[FROM table_name
WHERE CONDITION] ;](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-29-320.jpg)
![Here numerical_expression is used for mathematical expression or any formula. Following is a
simple examples showing usage of SQL Numeric Expressions:
SQL> SELECT (15 + 6) AS ADDITION
+----------+
| ADDITION |
+----------+
| 21 |
+----------+
1 row in set (0.00 sec)
There are several built-in functions like avg, sum, count, etc., to perform what is known as
aggregate data calculations against a table or a specific table column.
SQL> SELECT COUNT(*) AS "RECORDS" FROM CUSTOMERS;
+---------+
| RECORDS |
+---------+
| 7 |
+---------+
1 row in set (0.00 sec)
SQL - Date Expressions:
Date Expressions return current system date and time values:
SQL> SELECT CURRENT_TIMESTAMP;
+---------------------+
| Current_Timestamp |
+---------------------+
| 2009-11-12 06:40:23 |
+---------------------+
1 row in set (0.00 sec)
Another date expression is as follows:
SQL> SELECT GETDATE();;
+-------------------------+
| GETDATE |
+-------------------------+
| 2009-10-22 12:07:18.140 |
+-------------------------+
1 row in set (0.00 sec)
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![SQL - INSERT QUERYSQL - INSERT QUERY
The SQL INSERT INTO Statement is used to add new rows of data to a table in the database.
Syntax:
There are two basic syntaxes of INSERT INTO statement as follows:
INSERT INTO TABLE_NAME (column1, column2, column3,...columnN)]
VALUES (value1, value2, value3,...valueN);
Here, column1, column2,...columnN are the names of the columns in the table into which you want
to insert data.
You may not need to specify the columns name in the SQL query if you are adding values for all
the columns of the table. But make sure the order of the values is in the same order as the
columns in the table. The SQL INSERT INTO syntax would be as follows:
INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);
Example:
Following statements would create six records in CUSTOMERS table:
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, 'Ramesh', 32, 'Ahmedabad', 2000.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, 'Khilan', 25, 'Delhi', 1500.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, 'kaushik', 23, 'Kota', 2000.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, 'Chaitali', 25, 'Mumbai', 6500.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, 'Hardik', 27, 'Bhopal', 8500.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, 'Komal', 22, 'MP', 4500.00 );
You can create a record in CUSTOMERS table using second syntax as follows:
INSERT INTO CUSTOMERS
VALUES (7, 'Muffy', 24, 'Indore', 10000.00 );
All the above statements would produce the following records in CUSTOMERS table:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-33-320.jpg)
![Populate one table using another table:
You can populate data into a table through select statement over another table provided another
table has a set of fields, which are required to populate first table. Here is the syntax:
INSERT INTO first_table_name [(column1, column2, ... columnN)]
SELECT column1, column2, ...columnN
FROM second_table_name
[WHERE condition];
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![SQL - WHERE CLAUSESQL - WHERE CLAUSE
The SQL WHERE clause is used to specify a condition while fetching the data from single table or
joining with multiple tables.
If the given condition is satisfied then only it returns specific value from the table. You would use
WHERE clause to filter the records and fetching only necessary records.
The WHERE clause is not only used in SELECT statement, but it is also used in UPDATE, DELETE
statement, etc., which we would examine in subsequent chapters.
Syntax:
The basic syntax of SELECT statement with WHERE clause is as follows:
SELECT column1, column2, columnN
FROM table_name
WHERE [condition]
You can specify a condition using comparison or logical operators like >, <, =, LIKE, NOT, etc.
Below examples would make this concept clear.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table
where salary is greater than 2000:
SQL> SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000;
This would produce the following result:
+----+----------+----------+
| ID | NAME | SALARY |
+----+----------+----------+
| 4 | Chaitali | 6500.00 |
| 5 | Hardik | 8500.00 |
| 6 | Komal | 4500.00 |
| 7 | Muffy | 10000.00 |
+----+----------+----------+
Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table
for a customer with name Hardik. Here, it is important to note that all the strings should be given
inside single quotes ″ where as numeric values should be given without any quote as in above
example:](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-37-320.jpg)
![SQL> SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE NAME = 'Hardik';
This would produce the following result:
+----+----------+----------+
| ID | NAME | SALARY |
+----+----------+----------+
| 5 | Hardik | 8500.00 |
+----+----------+----------+
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![SQL - AND AND OR CONJUNCTIVE OPERATORSSQL - AND AND OR CONJUNCTIVE OPERATORS
The SQL AND and OR operators are used to combine multiple conditions to narrow data in an SQL
statement. These two operators are called conjunctive operators.
These operators provide a means to make multiple comparisons with different operators in the
same SQL statement.
The AND Operator:
The AND operator allows the existence of multiple conditions in an SQL statement's WHERE
clause.
Syntax:
The basic syntax of AND operator with WHERE clause is as follows:
SELECT column1, column2, columnN
FROM table_name
WHERE [condition1] AND [condition2]...AND [conditionN];
You can combine N number of conditions using AND operator. For an action to be taken by the SQL
statement, whether it be a transaction or query, all conditions separated by the AND must be
TRUE.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table
where salary is greater than 2000 AND age is less tan 25 years:
SQL> SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000 AND age < 25;
This would produce the following result:
+----+-------+----------+
| ID | NAME | SALARY |
+----+-------+----------+
| 6 | Komal | 4500.00 |
| 7 | Muffy | 10000.00 |
+----+-------+----------+
The OR Operator:
The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause.](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-39-320.jpg)
![Syntax:
The basic syntax of OR operator with WHERE clause is as follows:
SELECT column1, column2, columnN
FROM table_name
WHERE [condition1] OR [condition2]...OR [conditionN]
You can combine N number of conditions using OR operator. For an action to be taken by the SQL
statement, whether it be a transaction or query, only any ONE of the conditions separated by the
OR must be TRUE.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table
where salary is greater than 2000 OR age is less tan 25 years:
SQL> SELECT ID, NAME, SALARY
FROM CUSTOMERS
WHERE SALARY > 2000 OR age < 25;
This would produce the following result:
+----+----------+----------+
| ID | NAME | SALARY |
+----+----------+----------+
| 3 | kaushik | 2000.00 |
| 4 | Chaitali | 6500.00 |
| 5 | Hardik | 8500.00 |
| 6 | Komal | 4500.00 |
| 7 | Muffy | 10000.00 |
+----+----------+----------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-40-320.jpg)
![SQL - UPDATE QUERYSQL - UPDATE QUERY
The SQL UPDATE Query is used to modify the existing records in a table.
You can use WHERE clause with UPDATE query to update selected rows otherwise all the rows
would be affected.
Syntax:
The basic syntax of UPDATE query with WHERE clause is as follows:
UPDATE table_name
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];
You can combine N number of conditions using AND or OR operators.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would update ADDRESS for a customer whose ID is 6:
SQL> UPDATE CUSTOMERS
SET ADDRESS = 'Pune'
WHERE ID = 6;
Now, CUSTOMERS table would have the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | Pune | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
If you want to modify all ADDRESS and SALARY column values in CUSTOMERS table, you do not
need to use WHERE clause and UPDATE query would be as follows:
SQL> UPDATE CUSTOMERS
SET ADDRESS = 'Pune', SALARY = 1000.00;
Now, CUSTOMERS table would have the following records:](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-41-320.jpg)
![SQL - DELETE QUERYSQL - DELETE QUERY
The SQL DELETE Query is used to delete the existing records from a table.
You can use WHERE clause with DELETE query to delete selected rows, otherwise all the records
would be deleted.
Syntax:
The basic syntax of DELETE query with WHERE clause is as follows:
DELETE FROM table_name
WHERE [condition];
You can combine N number of conditions using AND or OR operators.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would DELETE a customer, whose ID is 6:
SQL> DELETE FROM CUSTOMERS
WHERE ID = 6;
Now, CUSTOMERS table would have the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
If you want to DELETE all the records from CUSTOMERS table, you do not need to use WHERE
clause and DELETE query would be as follows:
SQL> DELETE FROM CUSTOMERS;
Now, CUSTOMERS table would not have any record.](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-43-320.jpg)
![WHERE SALARY LIKE
'_2%3'
Finds any values that have a 2 in the second position and end with
a 3
WHERE SALARY LIKE
'2___3'
Finds any values in a five-digit number that start with 2 and end
with 3
Let us take a real example, consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would display all the records from CUSTOMERS table where
SALARY starts with 200:
SQL> SELECT * FROM CUSTOMERS
WHERE SALARY LIKE '200%';
This would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
+----+----------+-----+-----------+----------+
Loading [MathJax]/jax/output/HTML-CSS/jax.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-45-320.jpg)
![SQL - TOP, LIMIT OR ROWNUM CLAUSESQL - TOP, LIMIT OR ROWNUM CLAUSE
The SQL TOP clause is used to fetch a TOP N number or X percent records from a table.
Note: All the databases do not support TOP clause. For example MySQL supports LIMIT clause to
fetch limited number of records and Oracle uses ROWNUM to fetch limited number of records.
Syntax:
The basic syntax of TOP clause with SELECT statement would be as follows:
SELECT TOP number|percent column_name(s)
FROM table_name
WHERE [condition]
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example on SQL server, which would fetch top 3 records from CUSTOMERS table:
SQL> SELECT TOP 3 * FROM CUSTOMERS;
This would produce the following result:
+----+---------+-----+-----------+---------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+---------+-----+-----------+---------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
+----+---------+-----+-----------+---------+
If you are using MySQL server, then here is an equivalent example:
SQL> SELECT * FROM CUSTOMERS
LIMIT 3;
This would produce the following result:
+----+---------+-----+-----------+---------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+---------+-----+-----------+---------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
+----+---------+-----+-----------+---------+
If you are using Oracle server, then here is an equivalent example:](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-46-320.jpg)
![SQL - ORDER BY CLAUSESQL - ORDER BY CLAUSE
The SQL ORDER BY clause is used to sort the data in ascending or descending order, based on
one or more columns. Some database sorts query results in ascending order by default.
Syntax:
The basic syntax of ORDER BY clause is as follows:
SELECT column-list
FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];
You can use more than one column in the ORDER BY clause. Make sure whatever column you are
using to sort, that column should be in column-list.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would sort the result in ascending order by NAME and SALARY:
SQL> SELECT * FROM CUSTOMERS
ORDER BY NAME, SALARY;
This would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would sort the result in descending order by NAME:
SQL> SELECT * FROM CUSTOMERS
ORDER BY NAME DESC;
This would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-48-320.jpg)
![SQL - GROUP BYSQL - GROUP BY
The SQL GROUP BY clause is used in collaboration with the SELECT statement to arrange identical
data into groups.
The GROUP BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER
BY clause.
Syntax:
The basic syntax of GROUP BY clause is given below. The GROUP BY clause must follow the
conditions in the WHERE clause and must precede the ORDER BY clause if one is used.
SELECT column1, column2
FROM table_name
WHERE [ conditions ]
GROUP BY column1, column2
ORDER BY column1, column2
Example:
Consider the CUSTOMERS table is having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
If you want to know the total amount of salary on each customer, then GROUP BY query would be
as follows:
SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS
GROUP BY NAME;
This would produce the following result:
+----------+-------------+
| NAME | SUM(SALARY) |
+----------+-------------+
| Chaitali | 6500.00 |
| Hardik | 8500.00 |
| kaushik | 2000.00 |
| Khilan | 1500.00 |
| Komal | 4500.00 |
| Muffy | 10000.00 |
| Ramesh | 2000.00 |
+----------+-------------+
Now, let us have following table where CUSTOMERS table has the following records with duplicate
names:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-50-320.jpg)
![SQL - DISTINCT KEYWORDSQL - DISTINCT KEYWORD
The SQL DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the
duplicate records and fetching only unique records.
There may be a situation when you have multiple duplicate records in a table. While fetching such
records, it makes more sense to fetch only unique records instead of fetching duplicate records.
Syntax:
The basic syntax of DISTINCT keyword to eliminate duplicate records is as follows:
SELECT DISTINCT column1, column2,.....columnN
FROM table_name
WHERE [condition]
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
First, let us see how the following SELECT query returns duplicate salary records:
SQL> SELECT SALARY FROM CUSTOMERS
ORDER BY SALARY;
This would produce the following result where salary 2000 is coming twice which is a duplicate
record from the original table.
+----------+
| SALARY |
+----------+
| 1500.00 |
| 2000.00 |
| 2000.00 |
| 4500.00 |
| 6500.00 |
| 8500.00 |
| 10000.00 |
+----------+
Now, let us use DISTINCT keyword with the above SELECT query and see the result:
SQL> SELECT DISTINCT SALARY FROM CUSTOMERS
ORDER BY SALARY;
This would produce the following result where we do not have any duplicate entry:
+----------+
| SALARY |](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-52-320.jpg)
![SQL - SORTING RESULTSSQL - SORTING RESULTS
The SQL ORDER BY clause is used to sort the data in ascending or descending order, based on
one or more columns. Some database sorts query results in ascending order by default.
Syntax:
The basic syntax of ORDER BY clause which would be used to sort result in ascending or
descending order is as follows:
SELECT column-list
FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];
You can use more than one column in the ORDER BY clause. Make sure whatever column you are
using to sort, that column should be in column-list.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would sort the result in ascending order by NAME and SALARY:
SQL> SELECT * FROM CUSTOMERS
ORDER BY NAME, SALARY;
This would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
+----+----------+-----+-----------+----------+
Following is an example, which would sort the result in descending order by NAME:
SQL> SELECT * FROM CUSTOMERS
ORDER BY NAME DESC;
This would produce the following result:
+----+----------+-----+-----------+----------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-54-320.jpg)
![FULL JOIN: returns rows when there is a match in one of the tables.
SELF JOIN: is used to join a table to itself as if the table were two tables, temporarily renaming
at least one table in the SQL statement.
CARTESIAN JOIN: returns the Cartesian product of the sets of records from the two or more
joined tables.
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-57-320.jpg)
![+----+----------+--------+---------------------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-59-320.jpg)
![| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
| 5 | Hardik | NULL | NULL |
| 6 | Komal | NULL | NULL |
| 7 | Muffy | NULL | NULL |
+----+----------+--------+---------------------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-61-320.jpg)
![+------+----------+--------+---------------------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-63-320.jpg)
![| 5 | Hardik | NULL | NULL |
| 6 | Komal | NULL | NULL |
| 7 | Muffy | NULL | NULL |
| 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
+------+----------+--------+---------------------+
If your Database does not support FULL JOIN like MySQL does not support FULL JOIN, then you can
use UNION ALL clause to combine two JOINS as follows:
SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION ALL
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-65-320.jpg)
![+----+----------+---------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-67-320.jpg)
![SQL - CARTESIAN OR CROSS JOINSSQL - CARTESIAN OR CROSS JOINS
The CARTESIAN JOIN or CROSS JOIN returns the Cartesian product of the sets of records from
the two or more joined tables. Thus, it equates to an inner join where the join-condition always
evaluates to True or where the join-condition is absent from the statement.
Syntax:
The basic syntax of CARTESIAN JOIN or CROSS JOIN is as follows:
SELECT table1.column1, table2.column2...
FROM table1, table2 [, table3 ]
Example:
Consider the following two tables, a CUSTOMERS table is as follows:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
b Another table is ORDERS as follows:
+-----+---------------------+-------------+--------+
|OID | DATE | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 | 3 | 3000 |
| 100 | 2009-10-08 00:00:00 | 3 | 1500 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560 |
| 103 | 2008-05-20 00:00:00 | 4 | 2060 |
+-----+---------------------+-------------+--------+
Now, let us join these two tables using INNER JOIN as follows:
SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS, ORDERS;
This would produce the following result:
+----+----------+--------+---------------------+
| ID | NAME | AMOUNT | DATE |
+----+----------+--------+---------------------+
| 1 | Ramesh | 3000 | 2009-10-08 00:00:00 |
| 1 | Ramesh | 1500 | 2009-10-08 00:00:00 |
| 1 | Ramesh | 1560 | 2009-11-20 00:00:00 |
| 1 | Ramesh | 2060 | 2008-05-20 00:00:00 |
| 2 | Khilan | 3000 | 2009-10-08 00:00:00 |
| 2 | Khilan | 1500 | 2009-10-08 00:00:00 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 2 | Khilan | 2060 | 2008-05-20 00:00:00 |
| 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1560 | 2009-11-20 00:00:00 |
| 3 | kaushik | 2060 | 2008-05-20 00:00:00 |](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-68-320.jpg)
![| 4 | Chaitali | 3000 | 2009-10-08 00:00:00 |
| 4 | Chaitali | 1500 | 2009-10-08 00:00:00 |
| 4 | Chaitali | 1560 | 2009-11-20 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
| 5 | Hardik | 3000 | 2009-10-08 00:00:00 |
| 5 | Hardik | 1500 | 2009-10-08 00:00:00 |
| 5 | Hardik | 1560 | 2009-11-20 00:00:00 |
| 5 | Hardik | 2060 | 2008-05-20 00:00:00 |
| 6 | Komal | 3000 | 2009-10-08 00:00:00 |
| 6 | Komal | 1500 | 2009-10-08 00:00:00 |
| 6 | Komal | 1560 | 2009-11-20 00:00:00 |
| 6 | Komal | 2060 | 2008-05-20 00:00:00 |
| 7 | Muffy | 3000 | 2009-10-08 00:00:00 |
| 7 | Muffy | 1500 | 2009-10-08 00:00:00 |
| 7 | Muffy | 1560 | 2009-11-20 00:00:00 |
| 7 | Muffy | 2060 | 2008-05-20 00:00:00 |
+----+----------+--------+---------------------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-69-320.jpg)
![SQL - UNIONS CLAUSESQL - UNIONS CLAUSE
The SQL UNION clause/operator is used to combine the results of two or more SELECT statements
without returning any duplicate rows.
To use UNION, each SELECT must have the same number of columns selected, the same number
of column expressions, the same data type, and have them in the same order, but they do not
have to be the same length.
Syntax:
The basic syntax of UNION is as follows:
SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]
UNION
SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]
Here given condition could be any given expression based on your requirement.
Example:
Consider the following two tables, a CUSTOMERS table is as follows:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
b Another table is ORDERS as follows:
+-----+---------------------+-------------+--------+
|OID | DATE | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 | 3 | 3000 |
| 100 | 2009-10-08 00:00:00 | 3 | 1500 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560 |
| 103 | 2008-05-20 00:00:00 | 4 | 2060 |
+-----+---------------------+-------------+--------+
Now, let us join these two tables in our SELECT statement as follows:
SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-70-320.jpg)
![ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;
This would produce the following result:
+------+----------+--------+---------------------+
| ID | NAME | AMOUNT | DATE |
+------+----------+--------+---------------------+
| 1 | Ramesh | NULL | NULL |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
| 5 | Hardik | NULL | NULL |
| 6 | Komal | NULL | NULL |
| 7 | Muffy | NULL | NULL |
+------+----------+--------+---------------------+
The UNION ALL Clause:
The UNION ALL operator is used to combine the results of two SELECT statements including
duplicate rows.
The same rules that apply to UNION apply to the UNION ALL operator.
Syntax:
The basic syntax of UNION ALL is as follows:
SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]
UNION ALL
SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]
Here given condition could be any given expression based on your requirement.
Example:
Consider the following two tables, a CUSTOMERS table is as follows:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
b Another table is ORDERS as follows:
+-----+---------------------+-------------+--------+
|OID | DATE | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 | 3 | 3000 |
| 100 | 2009-10-08 00:00:00 | 3 | 1500 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560 |
| 103 | 2008-05-20 00:00:00 | 4 | 2060 |
+-----+---------------------+-------------+--------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-71-320.jpg)
![Now, let us join these two tables in our SELECT statement as follows:
SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION ALL
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;
This would produce the following result:
+------+----------+--------+---------------------+
| ID | NAME | AMOUNT | DATE |
+------+----------+--------+---------------------+
| 1 | Ramesh | NULL | NULL |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
| 5 | Hardik | NULL | NULL |
| 6 | Komal | NULL | NULL |
| 7 | Muffy | NULL | NULL |
| 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
| 3 | kaushik | 1500 | 2009-10-08 00:00:00 |
| 2 | Khilan | 1560 | 2009-11-20 00:00:00 |
| 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
+------+----------+--------+---------------------+
There are two other clauses i. e. , operators, which are very similar to UNION clause:
SQL INTERSECT Clause: is used to combine two SELECT statements, but returns rows only
from the first SELECT statement that are identical to a row in the second SELECT statement.
SQL EXCEPT Clause : combines two SELECT statements and returns rows from the first
SELECT statement that are not returned by the second SELECT statement.
Loading [MathJax]/jax/output/HTML-CSS/jax.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-72-320.jpg)
![SQL - ALIAS SYNTAXSQL - ALIAS SYNTAX
You can rename a table or a column temporarily by giving another name known as alias.
The use of table aliases means to rename a table in a particular SQL statement. The renaming is a
temporary change and the actual table name does not change in the database.
The column aliases are used to rename a table's columns for the purpose of a particular SQL
query.
Syntax:
The basic syntax of table alias is as follows:
SELECT column1, column2....
FROM table_name AS alias_name
WHERE [condition];
The basic syntax of column alias is as follows:
SELECT column_name AS alias_name
FROM table_name
WHERE [condition];
Example:
Consider the following two tables, a CUSTOMERS table is as follows:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
b Another table is ORDERS as follows:
+-----+---------------------+-------------+--------+
|OID | DATE | CUSTOMER_ID | AMOUNT |
+-----+---------------------+-------------+--------+
| 102 | 2009-10-08 00:00:00 | 3 | 3000 |
| 100 | 2009-10-08 00:00:00 | 3 | 1500 |
| 101 | 2009-11-20 00:00:00 | 2 | 1560 |
| 103 | 2008-05-20 00:00:00 | 4 | 2060 |
+-----+---------------------+-------------+--------+
Now, following is the usage of table alias:
SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT
FROM CUSTOMERS AS C, ORDERS AS O
WHERE C.ID = O.CUSTOMER_ID;
This would produce the following result:
+----+----------+-----+--------+
| ID | NAME | AGE | AMOUNT |](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-75-320.jpg)
![+----+----------+-----+--------+
| 3 | kaushik | 23 | 3000 |
| 3 | kaushik | 23 | 1500 |
| 2 | Khilan | 25 | 1560 |
| 4 | Chaitali | 25 | 2060 |
+----+----------+-----+--------+
Following is the usage of column alias:
SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME
FROM CUSTOMERS
WHERE SALARY IS NOT NULL;
This would produce the following result:
+-------------+---------------+
| CUSTOMER_ID | CUSTOMER_NAME |
+-------------+---------------+
| 1 | Ramesh |
| 2 | Khilan |
| 3 | kaushik |
| 4 | Chaitali |
| 5 | Hardik |
| 6 | Komal |
| 7 | Muffy |
+-------------+---------------+
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-76-320.jpg)
![The DROP INDEX Command:
An index can be dropped using SQL DROP command. Care should be taken when dropping an
index because performance may be slowed or improved.
The basic syntax is as follows:
DROP INDEX index_name;
You can check INDEX Constraint chapter to see actual examples on Indexes.
When should indexes be avoided?
Although indexes are intended to enhance a database's performance, there are times when they
should be avoided. The following guidelines indicate when the use of an index should be
reconsidered:
Indexes should not be used on small tables.
Tables that have frequent, large batch update or insert operations.
Indexes should not be used on columns that contain a high number of NULL values.
Columns that are frequently manipulated should not be indexed.
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-78-320.jpg)
![SQL - USING VIEWSSQL - USING VIEWS
A view is nothing more than a SQL statement that is stored in the database with an associated
name. A view is actually a composition of a table in the form of a predefined SQL query.
A view can contain all rows of a table or select rows from a table. A view can be created from one
or many tables which depends on the written SQL query to create a view.
Views, which are kind of virtual tables, allow users to do the following:
Structure data in a way that users or classes of users find natural or intuitive.
Restrict access to the data such that a user can see and sometimes modify exactly what they
need and no more.
Summarize data from various tables which can be used to generate reports.
Creating Views:
Database views are created using the CREATE VIEW statement. Views can be created from a
single table, multiple tables, or another view.
To create a view, a user must have the appropriate system privilege according to the specific
implementation.
The basic CREATE VIEW syntax is as follows:
CREATE VIEW view_name AS
SELECT column1, column2.....
FROM table_name
WHERE [condition];
You can include multiple tables in your SELECT statement in very similar way as you use them in
normal SQL SELECT query.
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Now, following is the example to create a view from CUSTOMERS table. This view would be used to
have customer name and age from CUSTOMERS table:
SQL > CREATE VIEW CUSTOMERS_VIEW AS
SELECT name, age
FROM CUSTOMERS;
Now, you can query CUSTOMERS_VIEW in similar way as you query an actual table. Following is the
example:
SQL > SELECT * FROM CUSTOMERS_VIEW;](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-82-320.jpg)
![This would ultimately update the base table CUSTOMERS and same would reflect in the view itself.
Now, try to query base table, and SELECT statement would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 35 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Inserting Rows into a View:
Rows of data can be inserted into a view. The same rules that apply to the UPDATE command also
apply to the INSERT command.
Here we can not insert rows in CUSTOMERS_VIEW because we have not included all the NOT NULL
columns in this view, otherwise you can insert rows in a view in similar way as you insert them in a
table.
Deleting Rows into a View:
Rows of data can be deleted from a view. The same rules that apply to the UPDATE and INSERT
commands apply to the DELETE command.
Following is an example to delete a record having AGE= 22.
SQL > DELETE FROM CUSTOMERS_VIEW
WHERE age = 22;
This would ultimately delete a row from the base table CUSTOMERS and same would reflect in the
view itself. Now, try to query base table, and SELECT statement would produce the following result:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 35 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Dropping Views:
Obviously, where you have a view, you need a way to drop the view if it is no longer needed. The
syntax is very simple as given below:
DROP VIEW view_name;
Following is an example to drop CUSTOMERS_VIEW from CUSTOMERS table:
DROP VIEW CUSTOMERS_VIEW;
Loading [MathJax]/jax/output/HTML-CSS/jax.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-84-320.jpg)
![SQL - HAVING CLAUSESQL - HAVING CLAUSE
The HAVING clause enables you to specify conditions that filter which group results appear in the
final results.
The WHERE clause places conditions on the selected columns, whereas the HAVING clause places
conditions on groups created by the GROUP BY clause.
Syntax:
The following is the position of the HAVING clause in a query:
SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY
The HAVING clause must follow the GROUP BY clause in a query and must also precede the ORDER
BY clause if used. The following is the syntax of the SELECT statement, including the HAVING
clause:
SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Following is the example, which would display record for which similar age count would be more
than or equal to 2:
SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY
FROM CUSTOMERS
GROUP BY age
HAVING COUNT(age) >= 2;
This would produce the following result:
+----+--------+-----+---------+---------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+--------+-----+---------+---------+
| 2 | Khilan | 25 | Delhi | 1500.00 |
+----+--------+-----+---------+---------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-85-320.jpg)
![1 row deleted.
Now that the three deletions have taken place, say you have changed your mind and decided to
ROLLBACK to the SAVEPOINT that you identified as SP2. Because SP2 was created after the first
deletion, the last two deletions are undone:
SQL> ROLLBACK TO SP2;
Rollback complete.
Notice that only the first deletion took place since you rolled back to SP2:
SQL> SELECT * FROM CUSTOMERS;
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
6 rows selected.
The RELEASE SAVEPOINT Command:
The RELEASE SAVEPOINT command is used to remove a SAVEPOINT that you have created.
The syntax for RELEASE SAVEPOINT is as follows:
RELEASE SAVEPOINT SAVEPOINT_NAME;
Once a SAVEPOINT has been released, you can no longer use the ROLLBACK command to undo
transactions performed since the SAVEPOINT.
The SET TRANSACTION Command:
The SET TRANSACTION command can be used to initiate a database transaction. This command is
used to specify characteristics for the transaction that follows.
For example, you can specify a transaction to be read only, or read write.
The syntax for SET TRANSACTION is as follows:
SET TRANSACTION [ READ WRITE | READ ONLY ];](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-90-320.jpg)
![SQL - SUB QUERIESSQL - SUB QUERIES
A Subquery or Inner query or Nested query is a query within another SQL query and embedded
within the WHERE clause.
A subquery is used to return data that will be used in the main query as a condition to further
restrict the data to be retrieved.
Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the
operators like =, <, >, >=, <=, IN, BETWEEN etc.
There are a few rules that subqueries must follow:
Subqueries must be enclosed within parentheses.
A subquery can have only one column in the SELECT clause, unless multiple columns are in
the main query for the subquery to compare its selected columns.
An ORDER BY cannot be used in a subquery, although the main query can use an ORDER BY.
The GROUP BY can be used to perform the same function as the ORDER BY in a subquery.
Subqueries that return more than one row can only be used with multiple value operators,
such as the IN operator.
The SELECT list cannot include any references to values that evaluate to a BLOB, ARRAY,
CLOB, or NCLOB.
A subquery cannot be immediately enclosed in a set function.
The BETWEEN operator cannot be used with a subquery; however, the BETWEEN operator
can be used within the subquery.
Subqueries with the SELECT Statement:
Subqueries are most frequently used with the SELECT statement. The basic syntax is as follows:
SELECT column_name [, column_name ]
FROM table1 [, table2 ]
WHERE column_name OPERATOR
(SELECT column_name [, column_name ]
FROM table1 [, table2 ]
[WHERE])
Example:
Consider the CUSTOMERS table having the following records:
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 35 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Now, let us check following subquery with SELECT statement:
SQL> SELECT *
FROM CUSTOMERS](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-91-320.jpg)
![WHERE ID IN (SELECT ID
FROM CUSTOMERS
WHERE SALARY > 4500) ;
This would produce the following result:
+----+----------+-----+---------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+---------+----------+
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+---------+----------+
Subqueries with the INSERT Statement:
Subqueries also can be used with INSERT statements. The INSERT statement uses the data
returned from the subquery to insert into another table. The selected data in the subquery can be
modified with any of the character, date or number functions.
The basic syntax is as follows:
INSERT INTO table_name [ (column1 [, column2 ]) ]
SELECT [ *|column1 [, column2 ]
FROM table1 [, table2 ]
[ WHERE VALUE OPERATOR ]
Example:
Consider a table CUSTOMERS_BKP with similar structure as CUSTOMERS table. Now to copy
complete CUSTOMERS table into CUSTOMERS_BKP, following is the syntax:
SQL> INSERT INTO CUSTOMERS_BKP
SELECT * FROM CUSTOMERS
WHERE ID IN (SELECT ID
FROM CUSTOMERS) ;
Subqueries with the UPDATE Statement:
The subquery can be used in conjunction with the UPDATE statement. Either single or multiple
columns in a table can be updated when using a subquery with the UPDATE statement.
The basic syntax is as follows:
UPDATE table
SET column_name = new_value
[ WHERE OPERATOR [ VALUE ]
(SELECT COLUMN_NAME
FROM TABLE_NAME)
[ WHERE) ]
Example:
Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.
Following example updates SALARY by 0.25 times in CUSTOMERS table for all the customers
whose AGE is greater than or equal to 27:
SQL> UPDATE CUSTOMERS
SET SALARY = SALARY * 0.25
WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP
WHERE AGE >= 27 );
This would impact two rows and finally CUSTOMERS table would have the following records:](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-92-320.jpg)
![+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 35 | Ahmedabad | 125.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 2125.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+
Subqueries with the DELETE Statement:
The subquery can be used in conjunction with the DELETE statement like with any other
statements mentioned above.
The basic syntax is as follows:
DELETE FROM TABLE_NAME
[ WHERE OPERATOR [ VALUE ]
(SELECT COLUMN_NAME
FROM TABLE_NAME)
[ WHERE) ]
Example:
Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table.
Following example deletes records from CUSTOMERS table for all the customers whose AGE is
greater than or equal to 27:
SQL> DELETE FROM CUSTOMERS
WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP
WHERE AGE > 27 );
This would impact two rows and finally CUSTOMERS table would have the following records:
+----+----------+-----+---------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+---------+----------+
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+---------+----------+](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-93-320.jpg)
![mysql_insert_id:
mysql_query ("INSERT INTO INSECT (name,date,origin)
VALUES('moth','2001-09-14','windowsill')", $conn_id);
$seq = mysql_insert_id ($conn_id);
Renumbering an Existing Sequence:
There may be a case when you have deleted many records from a table and you want to
resequence all the records. This can be done by using a simple trick but you should be very careful
to do so if your table is having join, with other table.
If you determine that resequencing an AUTO_INCREMENT column is unavoidable, the way to do it is
to drop the column from the table, then add it again. The following example shows how to
renumber the id values in the insect table using this technique:
mysql> ALTER TABLE INSECT DROP id;
mysql> ALTER TABLE insect
-> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST,
-> ADD PRIMARY KEY (id);
Starting a Sequence at a Particular Value:
By default, MySQL will start sequence from 1 but you can specify any other number as well at the
time of table creation. Following is the example where MySQL will start sequence from 100.
mysql> CREATE TABLE INSECT
-> (
-> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100,
-> PRIMARY KEY (id),
-> name VARCHAR(30) NOT NULL, # type of insect
-> date DATE NOT NULL, # date collected
-> origin VARCHAR(30) NOT NULL # where collected
);
Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE.
mysql> ALTER TABLE t AUTO_INCREMENT = 100;
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-95-320.jpg)
![SQL - INJECTIONSQL - INJECTION
If you take user input through a webpage and insert it into a SQL database, there's a chance that
you have left yourself wide open for a security issue known as SQL Injection.
This lesson will teach you how to help prevent this from happening and help you secure your
scripts and SQL statements in your server side scripts such as PERL Script.
Injection usually occurs when you ask a user for input, like their name, and instead of a name they
give you a SQL statement that you will unknowingly run on your database.
Never trust user provided data, process this data only after validation; as a rule, this is done by
pattern matching.
In the example below, the name is restricted to alphanumerical chars plus underscore and to a
length between 8 and 20 chars modifytheserulesasneeded.
if (preg_match("/^w{8,20}$/", $_GET['username'], $matches))
{
$result = mysql_query("SELECT * FROM CUSTOMERS
WHERE name=$matches[0]");
}
else
{
echo "user name not accepted";
}
To demonstrate the problem, consider this excerpt:
// supposed input
$name = "Qadir'; DELETE FROM CUSTOMERS;";
mysql_query("SELECT * FROM CUSTOMSRS WHERE name='{$name}'");
The function call is supposed to retrieve a record from the CUSTOMERS table where the name
column matches the name specified by the user. Under normal circumstances,
namewouldonlycontainalphanumericcharactersandperhapsspaces, suchasthestringilia. Buthere, byappendinganentirelynewqueryto
name, the call to the database turns into disaster: the injected DELETE query removes all records
from CUSTOMERS.
Fortunately, if you use MySQL, the mysql_query function does not permit query stacking or
executing multiple SQL queries in a single function call. If you try to stack queries, the call fails.
However, other PHP database extensions, such as SQLite and PostgreSQL, happily perform stacked
queries, executing all of the queries provided in one string and creating a serious security
problem.
Preventing SQL Injection:
You can handle all escape characters smartly in scripting languages like PERL and PHP. The MySQL
extension for PHP provides the function mysql_real_escape_string to escape input characters that
are special to MySQL.
if (get_magic_quotes_gpc())
{
$name = stripslashes($name);
}
$name = mysql_real_escape_string($name);
mysql_query("SELECT * FROM CUSTOMERS WHERE name='{$name}'");
The LIKE Quandary:
To address the LIKE quandary, a custom escaping mechanism must convert user-supplied '%' and
'_' characters to literals. Use addcslashes, a function that let's you specify a character range to
escape.](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-100-320.jpg)
![$sub = addcslashes(mysql_real_escape_string("%str"), "%_");
// $sub == %str_
mysql_query("SELECT * FROM messages
WHERE subject LIKE '{$sub}%'");
Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js](https://image.slidesharecdn.com/sqlcomplete-151220110332/85/SQL-Complete-Tutorial-All-Topics-Covered-101-320.jpg)
SQL Complete Tutorial. All Topics Covered
- 1. Made by: Danish Mehraj Microsoft Student Partner Email: [email protected] [email protected] Website: http://mspdanish.azurewebsites.net
- 2. SQL TUTORIALSQL TUTORIAL SQL is a database computer language designed for the retrieval and management of data in relational database. SQL stands for Structured Query Language. This tutorial will give you quick start with SQL. AUDIENCEAUDIENCE This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to SQL languages. PREREQUISITESPREREQUISITES Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about what is database, especially RDBMS and what is a computer programming language. COMPILE/EXECUTE SQL PROGRAMSCOMPILE/EXECUTE SQL PROGRAMS If you are willing to compile and execute SQL programs with Oracle 11g RDBMS but you do not have a setup for the same, then do not worry. The Coding Ground is available on a high end dedciated server giving you real programming experience. Yes! it is absolutely free and its online.
- 3. SQL - OVERVIEWSQL - OVERVIEW SQL tutorial gives unique learning on Structured Query Language and it helps to make practice on SQL commands which provides immediate results. SQL is a language of database, it includes database creation, deletion, fetching rows and modifying rows etc. SQL is an ANSI AmericanNationalStandardsInstitute standard but there are many different versions of the SQL language. What is SQL? SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database. SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language. Also, they are using different dialects, such as: MS SQL Server using T-SQL, Oracle using PL/SQL, MS Access version of SQL is called JET SQL nativeformat etc. Why SQL? Allows users to access data in relational database management systems. Allows users to describe the data. Allows users to define the data in database and manipulate that data. Allows to embed within other languages using SQL modules, libraries & pre-compilers. Allows users to create and drop databases and tables. Allows users to create view, stored procedure, functions in a database. Allows users to set permissions on tables, procedures, and views History: 1970 -- Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases. 1974 -- Structured Query Language appeared. 1978 -- IBM worked to develop Codd's ideas and released a product named System/R. 1986 -- IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software and its later becoming Oracle. SQL Process: When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task. There are various components included in the process. These components are Query Dispatcher, Optimization Engines, Classic Query Engine and SQL Query Engine, etc. Classic query engine handles all non-SQL queries but SQL query engine won't handle logical files.
- 4. Following is a simple diagram showing SQL Architecture: SQL Commands: The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE and DROP. These commands can be classified into groups based on their nature: DDL - Data Definition Language: Command Description CREATE Creates a new table, a view of a table, or other object in database ALTER Modifies an existing database object, such as a table. DROP Deletes an entire table, a view of a table or other object in the database. DML - Data Manipulation Language: Command Description SELECT Retrieves certain records from one or more tables INSERT Creates a record UPDATE Modifies records DELETE Deletes records DCL - Data Control Language:
- 5. Command Description GRANT Gives a privilege to user REVOKE Takes back privileges granted from user Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 6. SQL - RDBMS CONCEPTSSQL - RDBMS CONCEPTS What is RDBMS? RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. A Relational database management system RDBMS is a database management system DBMS that is based on the relational model as introduced by E. F. Codd. What is table? The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows. Remember, a table is the most common and simplest form of data storage in a relational database. Following is the example of a CUSTOMERS table: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ What is field? Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY. A field is a column in a table that is designed to maintain specific information about every record in the table. What is record or row? A record, also called a row of data, is each individual entry that exists in a table. For example there are 7 records in the above CUSTOMERS table. Following is a single row of data or record in the CUSTOMERS table: +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | +----+----------+-----+-----------+----------+ A record is a horizontal entity in a table. What is column? A column is a vertical entity in a table that contains all information associated with a specific field in a table. For example, a column in the CUSTOMERS table is ADDRESS, which represents location description and would consist of the following: +-----------+ | ADDRESS | +-----------+ | Ahmedabad |
- 7. | Delhi | | Kota | | Mumbai | | Bhopal | | MP | | Indore | +----+------+ What is NULL value? A NULL value in a table is a value in a field that appears to be blank, which means a field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation. SQL Constraints: Constraints are the rules enforced on data columns on table. These are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the database. Constraints could be column level or table level. Column level constraints are applied only to one column where as table level constraints are applied to the whole table. Following are commonly used constraints available in SQL: NOT NULL Constraint: Ensures that a column cannot have NULL value. DEFAULT Constraint: Provides a default value for a column when none is specified. UNIQUE Constraint: Ensures that all values in a column are different. PRIMARY Key: Uniquely identified each rows/records in a database table. FOREIGN Key: Uniquely identified a rows/records in any another database table. CHECK Constraint: The CHECK constraint ensures that all values in a column satisfy certain conditions. INDEX: Use to create and retrieve data from the database very quickly. Data Integrity: The following categories of the data integrity exist with each RDBMS: Entity Integrity: There are no duplicate rows in a table. Domain Integrity: Enforces valid entries for a given column by restricting the type, the format, or the range of values. Referential integrity: Rows cannot be deleted, which are used by other records. User-Defined Integrity: Enforces some specific business rules that do not fall into entity, domain or referential integrity. Database Normalization Database normalization is the process of efficiently organizing data in a database. There are two reasons of the normalization process: Eliminating redundant data, for example, storing the same data in more than one tables. Ensuring data dependencies make sense. Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored. Normalization consists of a series of guidelines that help guide you in creating a good database structure.
- 8. Normalization guidelines are divided into normal forms; think of form as the format or the way a database structure is laid out. The aim of normal forms is to organize the database structure so that it complies with the rules of first normal form, then second normal form, and finally third normal form. It's your choice to take it further and go to fourth normal form, fifth normal form, and so on, but generally speaking, third normal form is enough. First Normal Form 1NF Second Normal Form 2NF Third Normal Form 3NF Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 9. SQL - NOT NULL CONSTRAINTSQL - NOT NULL CONSTRAINT By default, a column can hold NULL values. If you do not want a column to have a NULL value, then you need to define such constraint on this column specifying that NULL is now not allowed for that column. A NULL is not the same as no data, rather, it represents unknown data. Example: For example, the following SQL creates a new table called CUSTOMERS and adds five columns, three of which, ID and NAME and AGE, specify not to accept NULLs: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); If CUSTOMERS table has already been created, then to add a NOT NULL constraint to SALARY column in Oracle and MySQL, you would write a statement similar to the following: ALTER TABLE CUSTOMERS MODIFY SALARY DECIMAL (18, 2) NOT NULL;
- 10. SQL - DEFAULT CONSTRAINTSQL - DEFAULT CONSTRAINT The DEFAULT constraint provides a default value to a column when the INSERT INTO statement does not provide a specific value. Example: For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here, SALARY column is set to 5000.00 by default, so in case INSERT INTO statement does not provide a value for this column, then by default this column would be set to 5000.00. CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2) DEFAULT 5000.00, PRIMARY KEY (ID) ); If CUSTOMERS table has already been created, then to add a DFAULT constraint to SALARY column, you would write a statement similar to the following: ALTER TABLE CUSTOMERS MODIFY SALARY DECIMAL (18, 2) DEFAULT 5000.00; Drop Default Constraint: To drop a DEFAULT constraint, use the following SQL: ALTER TABLE CUSTOMERS ALTER COLUMN SALARY DROP DEFAULT;
- 11. SQL - UNIQUE CONSTRAINTSQL - UNIQUE CONSTRAINT The UNIQUE Constraint prevents two records from having identical values in a particular column. In the CUSTOMERS table, for example, you might want to prevent two or more people from having identical age. Example: For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here, AGE column is set to UNIQUE, so that you can not have two records with same age: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL UNIQUE, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); If CUSTOMERS table has already been created, then to add a UNIQUE constraint to AGE column, you would write a statement similar to the following: ALTER TABLE CUSTOMERS MODIFY AGE INT NOT NULL UNIQUE; You can also use following syntax, which supports naming the constraint in multiple columns as well: ALTER TABLE CUSTOMERS ADD CONSTRAINT myUniqueConstraint UNIQUE(AGE, SALARY); DROP a UNIQUE Constraint: To drop a UNIQUE constraint, use the following SQL: ALTER TABLE CUSTOMERS DROP CONSTRAINT myUniqueConstraint; If you are using MySQL, then you can use the following syntax: ALTER TABLE CUSTOMERS DROP INDEX myUniqueConstraint;
- 12. SQL - PRIMARY KEYSQL - PRIMARY KEY A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields. When multiple fields are used as a primary key, they are called a composite key. If a table has a primary key defined on any fields, then you can not have two records having the same value of that fields. Note: You would use these concepts while creating database tables. Create Primary Key: Here is the syntax to define ID attribute as a primary key in a CUSTOMERS table. CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); To create a PRIMARY KEY constraint on the "ID" column when CUSTOMERS table already exists, use the following SQL syntax: ALTER TABLE CUSTOMER ADD PRIMARY KEY (ID); NOTE: If you use the ALTER TABLE statement to add a primary key, the primary key columns must already have been declared to not contain NULL values whenthetablewasfirstcreated. For defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID, NAME) ); To create a PRIMARY KEY constraint on the "ID" and "NAMES" columns when CUSTOMERS table already exists, use the following SQL syntax: ALTER TABLE CUSTOMERS ADD CONSTRAINT PK_CUSTID PRIMARY KEY (ID, NAME); Delete Primary Key: You can clear the primary key constraints from the table, Use Syntax: ALTER TABLE CUSTOMERS DROP PRIMARY KEY ; Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 13. SQL - FOREIGN KEYSQL - FOREIGN KEY A foreign key is a key used to link two tables together. This is sometimes called a referencing key. Foreign Key is a column or a combination of columns whose values match a Primary Key in a different table. The relationship between 2 tables matches the Primary Key in one of the tables with a Foreign Key in the second table. If a table has a primary key defined on any fields, then you can not have two records having the same value of that fields. Example: Consider the structure of the two tables as follows: CUSTOMERS table: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); ORDERS table: CREATE TABLE ORDERS ( ID INT NOT NULL, DATE DATETIME, CUSTOMER_ID INT references CUSTOMERS(ID), AMOUNT double, PRIMARY KEY (ID) ); If ORDERS table has already been created, and the foreign key has not yet been set, use the syntax for specifying a foreign key by altering a table. ALTER TABLE ORDERS ADD FOREIGN KEY (Customer_ID) REFERENCES CUSTOMERS (ID); DROP a FOREIGN KEY Constraint: To drop a FOREIGN KEY constraint, use the following SQL: ALTER TABLE ORDERS DROP FOREIGN KEY; Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 14. SQL - CHECK CONSTRAINTSQL - CHECK CONSTRAINT The CHECK Constraint enables a condition to check the value being entered into a record. If the condition evaluates to false, the record violates the constraint and isn't entered into the table. Example: For example, the following SQL creates a new table called CUSTOMERS and adds five columns. Here, we add a CHECK with AGE column, so that you can not have any CUSTOMER below 18 years: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL CHECK (AGE >= 18), ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); If CUSTOMERS table has already been created, then to add a CHECK constraint to AGE column, you would write a statement similar to the following: ALTER TABLE CUSTOMERS MODIFY AGE INT NOT NULL CHECK (AGE >= 18 ); You can also use following syntax, which supports naming the constraint in multiple columns as well: ALTER TABLE CUSTOMERS ADD CONSTRAINT myCheckConstraint CHECK(AGE >= 18); DROP a CHECK Constraint: To drop a CHECK constraint, use the following SQL. This syntax does not work with MySQL: ALTER TABLE CUSTOMERS DROP CONSTRAINT myCheckConstraint;
- 15. SQL - INDEX CONSTRAINTSQL - INDEX CONSTRAINT The INDEX is used to create and retrieve data from the database very quickly. Index can be created by using single or group of columns in a table. When index is created, it is assigned a ROWID for each row before it sorts out the data. Proper indexes are good for performance in large databases, but you need to be careful while creating index. Selection of fields depends on what you are using in your SQL queries. Example: For example, the following SQL creates a new table called CUSTOMERS and adds five columns: CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); Now, you can create index on single or multiple columns using the following syntax: CREATE INDEX index_name ON table_name ( column1, column2.....); To create an INDEX on AGE column, to optimize the search on customers for a particular age, following is the SQL syntax: CREATE INDEX idx_age ON CUSTOMERS ( AGE ); DROP an INDEX Constraint: To drop an INDEX constraint, use the following SQL: ALTER TABLE CUSTOMERS DROP INDEX idx_age;
- 16. SQL - RDBMS DATABASESSQL - RDBMS DATABASES There are many popular RDBMS available to work with. This tutorial gives a brief overview of few most popular RDBMS. This would help you to compare their basic features. MySQL MySQL is an open source SQL database, which is developed by Swedish company MySQL AB. MySQL is pronounced "my ess-que-ell," in contrast with SQL, pronounced "sequel." MySQL is supporting many different platforms including Microsoft Windows, the major Linux distributions, UNIX, and Mac OS X. MySQL has free and paid versions, depending on its usage non − commercial/commercial and features. MySQL comes with a very fast, multi-threaded, multi-user, and robust SQL database server. History: Development of MySQL by Michael Widenius & David Axmark beginning in 1994. First internal release on 23 May 1995. Windows version was released on 8 January 1998 for Windows 95 and NT. Version 3.23: beta from June 2000, production release January 2001. Version 4.0: beta from August 2002, production release March 2003 unions. Version 4.01: beta from August 2003, Jyoti adopts MySQL for database tracking. Version 4.1: beta from June 2004, production release October 2004. Version 5.0: beta from March 2005, production release October 2005. Sun Microsystems acquired MySQL AB on 26 February 2008. Version 5.1: production release 27 November 2008. Features: High Performance. High Availability. Scalability and Flexibility Run anything. Robust Transactional Support. Web and Data Warehouse Strengths. Strong Data Protection. Comprehensive Application Development. Management Ease. Open Source Freedom and 24 x 7 Support. Lowest Total Cost of Ownership. MS SQL Server MS SQL Server is a Relational Database Management System developed by Microsoft Inc. Its primary query languages are:
- 17. T-SQL. ANSI SQL. History: 1987 - Sybase releases SQL Server for UNIX. 1988 - Microsoft, Sybase, and Aston-Tate port SQL Server to OS/2. 1989 - Microsoft, Sybase, and Aston-Tate release SQL Server 1.0 for OS/2. 1990 - SQL Server 1.1 is released with support for Windows 3.0 clients. Aston - Tate drops out of SQL Server development. 2000 - Microsoft releases SQL Server 2000. 2001 - Microsoft releases XML for SQL Server Web Release 1 download. 2002 - Microsoft releases SQLXML 2.0 renamedfromXMLforSQLServer. 2002 - Microsoft releases SQLXML 3.0. 2005 - Microsoft releases SQL Server 2005 on November 7th, 2005. Features: High Performance. High Availability. Database mirroring. Database snapshots. CLR integration. Service Broker. DDL triggers. Ranking functions. Row version-based isolation levels. XML integration. TRY...CATCH. Database Mail. ORACLE It is a very large and multi-user database management system. Oracle is a relational database management system developed by 'Oracle Corporation'. Oracle works to efficiently manage its resource, a database of information, among the multiple clients requesting and sending data in the network. It is an excellent database server choice for client/server computing. Oracle supports all major operating systems for both clients and servers, including MSDOS, NetWare, UnixWare, OS/2 and most UNIX flavors. History: Oracle began in 1977 and celebrating its 32 wonderful years in the industry from1977to2009.
- 18. 1977 - Larry Ellison, Bob Miner and Ed Oates founded Software Development Laboratories to undertake development work. 1979 - Version 2.0 of Oracle was released and it became first commercial relational database and first SQL database. The company changed its name to Relational Software Inc. RSI. 1981 - RSI started developing tools for Oracle. 1982 - RSI was renamed to Oracle Corporation. 1983 - Oracle released version 3.0, rewritten in C language and ran on multiple platforms. 1984 - Oracle version 4.0 was released. It contained features like concurrency control - multi- version read consistency, etc. 1985 - Oracle version 4.0 was released. It contained features like concurrency control - multi- version read consistency, etc. 2007 - Oracle has released Oracle11g. The new version focused on better partitioning, easy migration etc. Features: Concurrency Read Consistency Locking Mechanisms Quiesce Database Portability Self-managing database SQL*Plus ASM Scheduler Resource Manager Data Warehousing Materialized views Bitmap indexes Table compression Parallel Execution Analytic SQL Data mining Partitioning MS ACCESS This is one of the most popular Microsoft products. Microsoft Access is an entry-level database management software. MS Access database is not only an inexpensive but also powerful database for small-scale projects. MS Access uses the Jet database engine, which utilizes a specific SQL language dialect sometimesreferredtoasJetSQL.
- 19. MS Access comes with the professional edition of MS Office package. MS Access has easy-to-use intuitive graphical interface. 1992 - Access version 1.0 was released. 1993 - Access 1.1 released to improve compatibility with inclusion the Access Basic programming language. The most significant transition was from Access 97 to Access 2000 2007 - Access 2007, a new database format was introduced ACCDB which supports complex data types such as multi valued and attachment fields. Features: Users can create tables, queries, forms and reports and connect them together with macros. The import and export of data to many formats including Excel, Outlook, ASCII, dBase, Paradox, FoxPro, SQL Server, Oracle, ODBC, etc. There is also the Jet Database format MDBorACCDBinAccess2007, which can contain the application and data in one file. This makes it very convenient to distribute the entire application to another user, who can run it in disconnected environments. Microsoft Access offers parameterized queries. These queries and Access tables can be referenced from other programs like VB6 and .NET through DAO or ADO. The desktop editions of Microsoft SQL Server can be used with Access as an alternative to the Jet Database Engine. Microsoft Access is a file server-based database. Unlike client-server relational database management systems RDBMS, Microsoft Access does not implement database triggers, stored procedures, or transaction logging. Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 20. SQL - SYNTAXSQL - SYNTAX SQL is followed by unique set of rules and guidelines called Syntax. This tutorial gives you a quick start with SQL by listing all the basic SQL Syntax: All the SQL statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE, ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon ; . Important point to be noted is that SQL is case insensitive, which means SELECT and select have same meaning in SQL statements, but MySQL makes difference in table names. So if you are working with MySQL, then you need to give table names as they exist in the database. All the examples given in this tutorial have been tested with MySQL server. SQL SELECT Statement: SELECT column1, column2....columnN FROM table_name; SQL DISTINCT Clause: SELECT DISTINCT column1, column2....columnN FROM table_name; SQL WHERE Clause: SELECT column1, column2....columnN FROM table_name WHERE CONDITION; SQL AND/OR Clause: SELECT column1, column2....columnN FROM table_name WHERE CONDITION-1 {AND|OR} CONDITION-2; SQL IN Clause: SELECT column1, column2....columnN FROM table_name WHERE column_name IN (val-1, val-2,...val-N); SQL BETWEEN Clause: SELECT column1, column2....columnN FROM table_name WHERE column_name BETWEEN val-1 AND val-2; SQL LIKE Clause: SELECT column1, column2....columnN FROM table_name WHERE column_name LIKE { PATTERN }; SQL ORDER BY Clause:
- 21. SELECT column1, column2....columnN FROM table_name WHERE CONDITION ORDER BY column_name {ASC|DESC}; SQL GROUP BY Clause: SELECT SUM(column_name) FROM table_name WHERE CONDITION GROUP BY column_name; SQL COUNT Clause: SELECT COUNT(column_name) FROM table_name WHERE CONDITION; SQL HAVING Clause: SELECT SUM(column_name) FROM table_name WHERE CONDITION GROUP BY column_name HAVING (arithematic function condition); SQL CREATE TABLE Statement: CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, ..... columnN datatype, PRIMARY KEY( one or more columns ) ); SQL DROP TABLE Statement: DROP TABLE table_name; SQL CREATE INDEX Statement : CREATE UNIQUE INDEX index_name ON table_name ( column1, column2,...columnN); SQL DROP INDEX Statement : ALTER TABLE table_name DROP INDEX index_name; SQL DESC Statement : DESC table_name; SQL TRUNCATE TABLE Statement: TRUNCATE TABLE table_name; SQL ALTER TABLE Statement:
- 22. ALTER TABLE table_name {ADD|DROP|MODIFY} column_name {data_ype}; SQL ALTER TABLE Statement Rename : ALTER TABLE table_name RENAME TO new_table_name; SQL INSERT INTO Statement: INSERT INTO table_name( column1, column2....columnN) VALUES ( value1, value2....valueN); SQL UPDATE Statement: UPDATE table_name SET column1 = value1, column2 = value2....columnN=valueN [ WHERE CONDITION ]; SQL DELETE Statement: DELETE FROM table_name WHERE {CONDITION}; SQL CREATE DATABASE Statement: CREATE DATABASE database_name; SQL DROP DATABASE Statement: DROP DATABASE database_name; SQL USE Statement: USE database_name; SQL COMMIT Statement: COMMIT; SQL ROLLBACK Statement: ROLLBACK; Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 23. SQL - DATA TYPESSQL - DATA TYPES SQL data type is an attribute that specifies type of data of any object. Each column, variable and expression has related data type in SQL. You would use these data types while creating your tables. You would choose a particular data type for a table column based on your requirement. SQL Server offers six categories of data types for your use: Exact Numeric Data Types: DATA TYPE FROM TO bigint -9,223,372,036,854,775,808 9,223,372,036,854,775,807 int -2,147,483,648 2,147,483,647 smallint -32,768 32,767 tinyint 0 255 bit 0 1 decimal -10^38 +1 10^38 -1 numeric -10^38 +1 10^38 -1 money -922,337,203,685,477.5808 +922,337,203,685,477.5807 smallmoney -214,748.3648 +214,748.3647 Approximate Numeric Data Types: DATA TYPE FROM TO float -1.79E + 308 1.79E + 308 real -3.40E + 38 3.40E + 38 Date and Time Data Types: DATA TYPE FROM TO datetime Jan 1, 1753 Dec 31, 9999 smalldatetime Jan 1, 1900 Jun 6, 2079 date Stores a date like June 30, 1991 time Stores a time of day like 12:30 P.M. Note: Here, datetime has 3.33 milliseconds accuracy where as smalldatetime has 1 minute accuracy. Character Strings Data Types:
- 24. DATA TYPE FROM TO char char Maximum length of 8,000 characters. Fixedlengthnon − Unicodecharacters varchar varchar Maximum of 8,000 characters. Variable − lengthnon − Unicodedata. varcharmax varcharmax Maximum length of 231characters, Variable-length non-Unicode data SQLServer2005only. text text Variable-length non-Unicode data with a maximum length of 2,147,483,647 characters. Unicode Character Strings Data Types: DATA TYPE Description nchar Maximum length of 4,000 characters.FixedlengthUnicode nvarchar Maximum length of 4,000 characters.VariablelengthUnicode nvarcharmax Maximum length of 231characters SQLServer2005only. VariablelengthUnicode ntext Maximum length of 1,073,741,823 characters. VariablelengthUnicode Binary Data Types: DATA TYPE Description binary Maximum length of 8,000 bytesFixed − lengthbinarydata varbinary Maximum length of 8,000 bytes.Variablelengthbinarydata varbinarymax Maximum length of 231 bytes SQLServer2005only. VariablelengthBinarydata image Maximum length of 2,147,483,647 bytes. VariablelengthBinaryData Misc Data Types: DATA TYPE Description sql_variant Stores values of various SQL Server-supported data types, except text, ntext, and timestamp. timestamp Stores a database-wide unique number that gets updated every time a row gets updated uniqueidentifier Stores a globally unique identifier GUID xml Stores XML data. You can store xml instances in a column or a
- 25. variable SQLServer2005only. cursor Reference to a cursor object table Stores a result set for later processing Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 26. SQL - OPERATORSSQL - OPERATORS What is an Operator in SQL? An operator is a reserved word or a character used primarily in an SQL statement's WHERE clause to perform operations, such as comparisons and arithmetic operations. Operators are used to specify conditions in an SQL statement and to serve as conjunctions for multiple conditions in a statement. Arithmetic operators Comparison operators Logical operators Operators used to negate conditions SQL Arithmetic Operators: Assume variable a holds 10 and variable b holds 20, then: Show Examples Operator Description Example + Addition - Adds values on either side of the operator a + b will give 30 - Subtraction - Subtracts right hand operand from left hand operand a - b will give -10 * Multiplication - Multiplies values on either side of the operator a * b will give 200 / Division - Divides left hand operand by right hand operand b / a will give 2 % Modulus - Divides left hand operand by right hand operand and returns remainder b % a will give 0 SQL Comparison Operators: Assume variable a holds 10 and variable b holds 20, then: Show Examples Operator Description Example = Checks if the values of two operands are equal or not, if yes then condition becomes true. a = b is not true. != Checks if the values of two operands are equal or not, if values are not equal then condition becomes true. a! = b is true. <> Checks if the values of two operands are equal or not, if values are not equal then a <> b is true.
- 27. condition becomes true. > Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. a > b is not true. < Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. a < b is true. >= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. a >= b is not true. <= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. a <= b is true. !< Checks if the value of left operand is not less than the value of right operand, if yes then condition becomes true. a! < b is false. !> Checks if the value of left operand is not greater than the value of right operand, if yes then condition becomes true. a! > b is true. SQL Logical Operators: Here is a list of all the logical operators available in SQL. Show Examples Operator Description ALL The ALL operator is used to compare a value to all values in another value set. AND The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause. ANY The ANY operator is used to compare a value to any applicable value in the list according to the condition. BETWEEN The BETWEEN operator is used to search for values that are within a set of values, given the minimum value and the maximum value. EXISTS The EXISTS operator is used to search for the presence of a row in a specified table that meets certain criteria. IN The IN operator is used to compare a value to a list of literal values that have been specified. LIKE The LIKE operator is used to compare a value to similar values using wildcard operators. NOT The NOT operator reverses the meaning of the logical operator with which it is used. Eg: NOT EXISTS, NOT BETWEEN, NOT IN, etc. This is a negate operator. OR The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause. IS NULL The NULL operator is used to compare a value with a NULL value.
- 28. UNIQUE The UNIQUE operator searches every row of a specified table for uniqueness noduplicates. Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 29. SQL - EXPRESSIONSSQL - EXPRESSIONS An expression is a combination of one or more values, operators, and SQL functions that evaluate to a value. SQL EXPRESSIONs are like formulas and they are written in query language. You can also use them to query the database for specific set of data. Syntax: Consider the basic syntax of the SELECT statement as follows: SELECT column1, column2, columnN FROM table_name WHERE [CONDITION|EXPRESSION]; There are different types of SQL expressions, which are mentioned below: SQL - Boolean Expressions: SQL Boolean Expressions fetch the data on the basis of matching single value. Following is the syntax: SELECT column1, column2, columnN FROM table_name WHERE SINGLE VALUE MATCHTING EXPRESSION; Consider the CUSTOMERS table having the following records: SQL> SELECT * FROM CUSTOMERS; +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ 7 rows in set (0.00 sec) Here is simple example showing usage of SQL Boolean Expressions: SQL> SELECT * FROM CUSTOMERS WHERE SALARY = 10000; +----+-------+-----+---------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+-------+-----+---------+----------+ | 7 | Muffy | 24 | Indore | 10000.00 | +----+-------+-----+---------+----------+ 1 row in set (0.00 sec) SQL - Numeric Expression: This expression is used to perform any mathematical operation in any query. Following is the syntax: SELECT numerical_expression as OPERATION_NAME [FROM table_name WHERE CONDITION] ;
- 30. Here numerical_expression is used for mathematical expression or any formula. Following is a simple examples showing usage of SQL Numeric Expressions: SQL> SELECT (15 + 6) AS ADDITION +----------+ | ADDITION | +----------+ | 21 | +----------+ 1 row in set (0.00 sec) There are several built-in functions like avg, sum, count, etc., to perform what is known as aggregate data calculations against a table or a specific table column. SQL> SELECT COUNT(*) AS "RECORDS" FROM CUSTOMERS; +---------+ | RECORDS | +---------+ | 7 | +---------+ 1 row in set (0.00 sec) SQL - Date Expressions: Date Expressions return current system date and time values: SQL> SELECT CURRENT_TIMESTAMP; +---------------------+ | Current_Timestamp | +---------------------+ | 2009-11-12 06:40:23 | +---------------------+ 1 row in set (0.00 sec) Another date expression is as follows: SQL> SELECT GETDATE();; +-------------------------+ | GETDATE | +-------------------------+ | 2009-10-22 12:07:18.140 | +-------------------------+ 1 row in set (0.00 sec) Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 31. SQL - CREATE DATABASESQL - CREATE DATABASE The SQL CREATE DATABASE statement is used to create new SQL database. Syntax: Basic syntax of CREATE DATABASE statement is as follows: CREATE DATABASE DatabaseName; Always database name should be unique within the RDBMS. Example: If you want to create new database <testDB>, then CREATE DATABASE statement would be as follows: SQL> CREATE DATABASE testDB; Make sure you have admin privilege before creating any database. Once a database is created, you can check it in the list of databases as follows: SQL> SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | AMROOD | | TUTORIALSPOINT | | mysql | | orig | | test | | testDB | +--------------------+ 7 rows in set (0.00 sec)
- 32. SQL - DROP OR DELETE DATABASESQL - DROP OR DELETE DATABASE The SQL DROP DATABASE statement is used to drop an existing database in SQL schema. Syntax: Basic syntax of DROP DATABASE statement is as follows: DROP DATABASE DatabaseName; Always database name should be unique within the RDBMS. Example: If you want to delete an existing database <testDB>, then DROP DATABASE statement would be as follows: SQL> DROP DATABASE testDB; NOTE: Be careful before using this operation because by deleting an existing database would result in loss of complete information stored in the database. Make sure you have admin privilege before dropping any database. Once a database is dropped, you can check it in the list of databases as follows: SQL> SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | AMROOD | | TUTORIALSPOINT | | mysql | | orig | | test | +--------------------+ 6 rows in set (0.00 sec)
- 33. SQL - INSERT QUERYSQL - INSERT QUERY The SQL INSERT INTO Statement is used to add new rows of data to a table in the database. Syntax: There are two basic syntaxes of INSERT INTO statement as follows: INSERT INTO TABLE_NAME (column1, column2, column3,...columnN)] VALUES (value1, value2, value3,...valueN); Here, column1, column2,...columnN are the names of the columns in the table into which you want to insert data. You may not need to specify the columns name in the SQL query if you are adding values for all the columns of the table. But make sure the order of the values is in the same order as the columns in the table. The SQL INSERT INTO syntax would be as follows: INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN); Example: Following statements would create six records in CUSTOMERS table: INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (1, 'Ramesh', 32, 'Ahmedabad', 2000.00 ); INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (2, 'Khilan', 25, 'Delhi', 1500.00 ); INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (3, 'kaushik', 23, 'Kota', 2000.00 ); INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (4, 'Chaitali', 25, 'Mumbai', 6500.00 ); INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (5, 'Hardik', 27, 'Bhopal', 8500.00 ); INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY) VALUES (6, 'Komal', 22, 'MP', 4500.00 ); You can create a record in CUSTOMERS table using second syntax as follows: INSERT INTO CUSTOMERS VALUES (7, 'Muffy', 24, 'Indore', 10000.00 ); All the above statements would produce the following records in CUSTOMERS table: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+
- 34. Populate one table using another table: You can populate data into a table through select statement over another table provided another table has a set of fields, which are required to populate first table. Here is the syntax: INSERT INTO first_table_name [(column1, column2, ... columnN)] SELECT column1, column2, ...columnN FROM second_table_name [WHERE condition]; Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 35. SQL - SELECT QUERYSQL - SELECT QUERY SQL SELECT statement is used to fetch the data from a database table which returns data in the form of result table. These result tables are called result-sets. Syntax: The basic syntax of SELECT statement is as follows: SELECT column1, column2, columnN FROM table_name; Here, column1, column2...are the fields of a table whose values you want to fetch. If you want to fetch all the fields available in the field, then you can use the following syntax: SELECT * FROM table_name; Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would fetch ID, Name and Salary fields of the customers available in CUSTOMERS table: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS; This would produce the following result: +----+----------+----------+ | ID | NAME | SALARY | +----+----------+----------+ | 1 | Ramesh | 2000.00 | | 2 | Khilan | 1500.00 | | 3 | kaushik | 2000.00 | | 4 | Chaitali | 6500.00 | | 5 | Hardik | 8500.00 | | 6 | Komal | 4500.00 | | 7 | Muffy | 10000.00 | +----+----------+----------+ If you want to fetch all the fields of CUSTOMERS table, then use the following query: SQL> SELECT * FROM CUSTOMERS; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+
- 36. | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+
- 37. SQL - WHERE CLAUSESQL - WHERE CLAUSE The SQL WHERE clause is used to specify a condition while fetching the data from single table or joining with multiple tables. If the given condition is satisfied then only it returns specific value from the table. You would use WHERE clause to filter the records and fetching only necessary records. The WHERE clause is not only used in SELECT statement, but it is also used in UPDATE, DELETE statement, etc., which we would examine in subsequent chapters. Syntax: The basic syntax of SELECT statement with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name WHERE [condition] You can specify a condition using comparison or logical operators like >, <, =, LIKE, NOT, etc. Below examples would make this concept clear. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000; This would produce the following result: +----+----------+----------+ | ID | NAME | SALARY | +----+----------+----------+ | 4 | Chaitali | 6500.00 | | 5 | Hardik | 8500.00 | | 6 | Komal | 4500.00 | | 7 | Muffy | 10000.00 | +----+----------+----------+ Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table for a customer with name Hardik. Here, it is important to note that all the strings should be given inside single quotes ″ where as numeric values should be given without any quote as in above example:
- 38. SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE NAME = 'Hardik'; This would produce the following result: +----+----------+----------+ | ID | NAME | SALARY | +----+----------+----------+ | 5 | Hardik | 8500.00 | +----+----------+----------+ Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 39. SQL - AND AND OR CONJUNCTIVE OPERATORSSQL - AND AND OR CONJUNCTIVE OPERATORS The SQL AND and OR operators are used to combine multiple conditions to narrow data in an SQL statement. These two operators are called conjunctive operators. These operators provide a means to make multiple comparisons with different operators in the same SQL statement. The AND Operator: The AND operator allows the existence of multiple conditions in an SQL statement's WHERE clause. Syntax: The basic syntax of AND operator with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name WHERE [condition1] AND [condition2]...AND [conditionN]; You can combine N number of conditions using AND operator. For an action to be taken by the SQL statement, whether it be a transaction or query, all conditions separated by the AND must be TRUE. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000 AND age is less tan 25 years: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000 AND age < 25; This would produce the following result: +----+-------+----------+ | ID | NAME | SALARY | +----+-------+----------+ | 6 | Komal | 4500.00 | | 7 | Muffy | 10000.00 | +----+-------+----------+ The OR Operator: The OR operator is used to combine multiple conditions in an SQL statement's WHERE clause.
- 40. Syntax: The basic syntax of OR operator with WHERE clause is as follows: SELECT column1, column2, columnN FROM table_name WHERE [condition1] OR [condition2]...OR [conditionN] You can combine N number of conditions using OR operator. For an action to be taken by the SQL statement, whether it be a transaction or query, only any ONE of the conditions separated by the OR must be TRUE. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would fetch ID, Name and Salary fields from the CUSTOMERS table where salary is greater than 2000 OR age is less tan 25 years: SQL> SELECT ID, NAME, SALARY FROM CUSTOMERS WHERE SALARY > 2000 OR age < 25; This would produce the following result: +----+----------+----------+ | ID | NAME | SALARY | +----+----------+----------+ | 3 | kaushik | 2000.00 | | 4 | Chaitali | 6500.00 | | 5 | Hardik | 8500.00 | | 6 | Komal | 4500.00 | | 7 | Muffy | 10000.00 | +----+----------+----------+
- 41. SQL - UPDATE QUERYSQL - UPDATE QUERY The SQL UPDATE Query is used to modify the existing records in a table. You can use WHERE clause with UPDATE query to update selected rows otherwise all the rows would be affected. Syntax: The basic syntax of UPDATE query with WHERE clause is as follows: UPDATE table_name SET column1 = value1, column2 = value2...., columnN = valueN WHERE [condition]; You can combine N number of conditions using AND or OR operators. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would update ADDRESS for a customer whose ID is 6: SQL> UPDATE CUSTOMERS SET ADDRESS = 'Pune' WHERE ID = 6; Now, CUSTOMERS table would have the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | Pune | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ If you want to modify all ADDRESS and SALARY column values in CUSTOMERS table, you do not need to use WHERE clause and UPDATE query would be as follows: SQL> UPDATE CUSTOMERS SET ADDRESS = 'Pune', SALARY = 1000.00; Now, CUSTOMERS table would have the following records:
- 42. +----+----------+-----+---------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+---------+---------+ | 1 | Ramesh | 32 | Pune | 1000.00 | | 2 | Khilan | 25 | Pune | 1000.00 | | 3 | kaushik | 23 | Pune | 1000.00 | | 4 | Chaitali | 25 | Pune | 1000.00 | | 5 | Hardik | 27 | Pune | 1000.00 | | 6 | Komal | 22 | Pune | 1000.00 | | 7 | Muffy | 24 | Pune | 1000.00 | +----+----------+-----+---------+---------+
- 43. SQL - DELETE QUERYSQL - DELETE QUERY The SQL DELETE Query is used to delete the existing records from a table. You can use WHERE clause with DELETE query to delete selected rows, otherwise all the records would be deleted. Syntax: The basic syntax of DELETE query with WHERE clause is as follows: DELETE FROM table_name WHERE [condition]; You can combine N number of conditions using AND or OR operators. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would DELETE a customer, whose ID is 6: SQL> DELETE FROM CUSTOMERS WHERE ID = 6; Now, CUSTOMERS table would have the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ If you want to DELETE all the records from CUSTOMERS table, you do not need to use WHERE clause and DELETE query would be as follows: SQL> DELETE FROM CUSTOMERS; Now, CUSTOMERS table would not have any record.
- 44. SQL - LIKE CLAUSESQL - LIKE CLAUSE The SQL LIKE clause is used to compare a value to similar values using wildcard operators. There are two wildcards used in conjunction with the LIKE operator: The percent sign The underscore _ The percent sign represents zero, one, or multiple characters. The underscore represents a single number or character. The symbols can be used in combinations. Syntax: The basic syntax of % and _ is as follows: SELECT FROM table_name WHERE column LIKE 'XXXX%' or SELECT FROM table_name WHERE column LIKE '%XXXX%' or SELECT FROM table_name WHERE column LIKE 'XXXX_' or SELECT FROM table_name WHERE column LIKE '_XXXX' or SELECT FROM table_name WHERE column LIKE '_XXXX_' You can combine N number of conditions using AND or OR operators. Here, XXXX could be any numeric or string value. Example: Here are number of examples showing WHERE part having different LIKE clause with '%' and '_' operators: Statement Description WHERE SALARY LIKE '200%' Finds any values that start with 200 WHERE SALARY LIKE '%200%' Finds any values that have 200 in any position WHERE SALARY LIKE '_00%' Finds any values that have 00 in the second and third positions WHERE SALARY LIKE '2_%_%' Finds any values that start with 2 and are at least 3 characters in length WHERE SALARY LIKE '%2' Finds any values that end with 2
- 45. WHERE SALARY LIKE '_2%3' Finds any values that have a 2 in the second position and end with a 3 WHERE SALARY LIKE '2___3' Finds any values in a five-digit number that start with 2 and end with 3 Let us take a real example, consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would display all the records from CUSTOMERS table where SALARY starts with 200: SQL> SELECT * FROM CUSTOMERS WHERE SALARY LIKE '200%'; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 3 | kaushik | 23 | Kota | 2000.00 | +----+----------+-----+-----------+----------+ Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 46. SQL - TOP, LIMIT OR ROWNUM CLAUSESQL - TOP, LIMIT OR ROWNUM CLAUSE The SQL TOP clause is used to fetch a TOP N number or X percent records from a table. Note: All the databases do not support TOP clause. For example MySQL supports LIMIT clause to fetch limited number of records and Oracle uses ROWNUM to fetch limited number of records. Syntax: The basic syntax of TOP clause with SELECT statement would be as follows: SELECT TOP number|percent column_name(s) FROM table_name WHERE [condition] Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example on SQL server, which would fetch top 3 records from CUSTOMERS table: SQL> SELECT TOP 3 * FROM CUSTOMERS; This would produce the following result: +----+---------+-----+-----------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+---------+-----+-----------+---------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | +----+---------+-----+-----------+---------+ If you are using MySQL server, then here is an equivalent example: SQL> SELECT * FROM CUSTOMERS LIMIT 3; This would produce the following result: +----+---------+-----+-----------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+---------+-----+-----------+---------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | +----+---------+-----+-----------+---------+ If you are using Oracle server, then here is an equivalent example:
- 47. SQL> SELECT * FROM CUSTOMERS WHERE ROWNUM <= 3; This would produce the following result: +----+---------+-----+-----------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+---------+-----+-----------+---------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | +----+---------+-----+-----------+---------+
- 48. SQL - ORDER BY CLAUSESQL - ORDER BY CLAUSE The SQL ORDER BY clause is used to sort the data in ascending or descending order, based on one or more columns. Some database sorts query results in ascending order by default. Syntax: The basic syntax of ORDER BY clause is as follows: SELECT column-list FROM table_name [WHERE condition] [ORDER BY column1, column2, .. columnN] [ASC | DESC]; You can use more than one column in the ORDER BY clause. Make sure whatever column you are using to sort, that column should be in column-list. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would sort the result in ascending order by NAME and SALARY: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME, SALARY; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would sort the result in descending order by NAME: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME DESC; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY |
- 49. +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 7 | Muffy | 24 | Indore | 10000.00 | | 6 | Komal | 22 | MP | 4500.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | +----+----------+-----+-----------+----------+
- 50. SQL - GROUP BYSQL - GROUP BY The SQL GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. The GROUP BY clause follows the WHERE clause in a SELECT statement and precedes the ORDER BY clause. Syntax: The basic syntax of GROUP BY clause is given below. The GROUP BY clause must follow the conditions in the WHERE clause and must precede the ORDER BY clause if one is used. SELECT column1, column2 FROM table_name WHERE [ conditions ] GROUP BY column1, column2 ORDER BY column1, column2 Example: Consider the CUSTOMERS table is having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ If you want to know the total amount of salary on each customer, then GROUP BY query would be as follows: SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS GROUP BY NAME; This would produce the following result: +----------+-------------+ | NAME | SUM(SALARY) | +----------+-------------+ | Chaitali | 6500.00 | | Hardik | 8500.00 | | kaushik | 2000.00 | | Khilan | 1500.00 | | Komal | 4500.00 | | Muffy | 10000.00 | | Ramesh | 2000.00 | +----------+-------------+ Now, let us have following table where CUSTOMERS table has the following records with duplicate names: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+
- 51. | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Ramesh | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | kaushik | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Now again, if you want to know the total amount of salary on each customer, then GROUP BY query would be as follows: SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS GROUP BY NAME; This would produce the following result: +---------+-------------+ | NAME | SUM(SALARY) | +---------+-------------+ | Hardik | 8500.00 | | kaushik | 8500.00 | | Komal | 4500.00 | | Muffy | 10000.00 | | Ramesh | 3500.00 | +---------+-------------+
- 52. SQL - DISTINCT KEYWORDSQL - DISTINCT KEYWORD The SQL DISTINCT keyword is used in conjunction with SELECT statement to eliminate all the duplicate records and fetching only unique records. There may be a situation when you have multiple duplicate records in a table. While fetching such records, it makes more sense to fetch only unique records instead of fetching duplicate records. Syntax: The basic syntax of DISTINCT keyword to eliminate duplicate records is as follows: SELECT DISTINCT column1, column2,.....columnN FROM table_name WHERE [condition] Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ First, let us see how the following SELECT query returns duplicate salary records: SQL> SELECT SALARY FROM CUSTOMERS ORDER BY SALARY; This would produce the following result where salary 2000 is coming twice which is a duplicate record from the original table. +----------+ | SALARY | +----------+ | 1500.00 | | 2000.00 | | 2000.00 | | 4500.00 | | 6500.00 | | 8500.00 | | 10000.00 | +----------+ Now, let us use DISTINCT keyword with the above SELECT query and see the result: SQL> SELECT DISTINCT SALARY FROM CUSTOMERS ORDER BY SALARY; This would produce the following result where we do not have any duplicate entry: +----------+ | SALARY |
- 53. +----------+ | 1500.00 | | 2000.00 | | 4500.00 | | 6500.00 | | 8500.00 | | 10000.00 | +----------+
- 54. SQL - SORTING RESULTSSQL - SORTING RESULTS The SQL ORDER BY clause is used to sort the data in ascending or descending order, based on one or more columns. Some database sorts query results in ascending order by default. Syntax: The basic syntax of ORDER BY clause which would be used to sort result in ascending or descending order is as follows: SELECT column-list FROM table_name [WHERE condition] [ORDER BY column1, column2, .. columnN] [ASC | DESC]; You can use more than one column in the ORDER BY clause. Make sure whatever column you are using to sort, that column should be in column-list. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would sort the result in ascending order by NAME and SALARY: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME, SALARY; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | +----+----------+-----+-----------+----------+ Following is an example, which would sort the result in descending order by NAME: SQL> SELECT * FROM CUSTOMERS ORDER BY NAME DESC; This would produce the following result: +----+----------+-----+-----------+----------+
- 55. | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 7 | Muffy | 24 | Indore | 10000.00 | | 6 | Komal | 22 | MP | 4500.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | +----+----------+-----+-----------+----------+ To fetch the rows with own preferred order, the SELECT query would as follows: SQL> SELECT * FROM CUSTOMERS ORDER BY (CASE ADDRESS WHEN 'DELHI' THEN 1 WHEN 'BHOPAL' THEN 2 WHEN 'KOTA' THEN 3 WHEN 'AHMADABAD' THEN 4 WHEN 'MP' THEN 5 ELSE 100 END) ASC, ADDRESS DESC; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 2 | Khilan | 25 | Delhi | 1500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 6 | Komal | 22 | MP | 4500.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | +----+----------+-----+-----------+----------+ This will sort customers by ADDRESS in your ownoOrder of preference first and in a natural order for the remaining addresses. Also remaining Addresses will be sorted in the reverse alpha order.
- 56. SQL - USING JOINSSQL - USING JOINS The SQL Joins clause is used to combine records from two or more tables in a database. A JOIN is a means for combining fields from two tables by using values common to each. Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables in our SELECT statement as follows: SQL> SELECT ID, NAME, AGE, AMOUNT FROM CUSTOMERS, ORDERS WHERE CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +----+----------+-----+--------+ | ID | NAME | AGE | AMOUNT | +----+----------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Khilan | 25 | 1560 | | 4 | Chaitali | 25 | 2060 | +----+----------+-----+--------+ Here, it is noticeable that the join is performed in the WHERE clause. Several operators can be used to join tables, such as =, <, >, <>, <=, >=, !=, BETWEEN, LIKE, and NOT; they can all be used to join tables. However, the most common operator is the equal symbol. SQL Join Types: There are different types of joins available in SQL: INNER JOIN: returns rows when there is a match in both tables. LEFT JOIN: returns all rows from the left table, even if there are no matches in the right table. RIGHT JOIN: returns all rows from the right table, even if there are no matches in the left table.
- 57. FULL JOIN: returns rows when there is a match in one of the tables. SELF JOIN: is used to join a table to itself as if the table were two tables, temporarily renaming at least one table in the SQL statement. CARTESIAN JOIN: returns the Cartesian product of the sets of records from the two or more joined tables. Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 58. SQL - INNER JOINSSQL - INNER JOINS The most frequently used and important of the joins is the INNER JOIN. They are also referred to as an EQUIJOIN. The INNER JOIN creates a new result table by combining column values of two tables table1andtable2 based upon the join-predicate. The query compares each row of table1 with each row of table2 to find all pairs of rows which satisfy the join-predicate. When the join-predicate is satisfied, column values for each matched pair of rows of A and B are combined into a result row. Syntax: The basic syntax of INNER JOIN is as follows: SELECT table1.column1, table2.column2... FROM table1 INNER JOIN table2 ON table1.common_field = table2.common_field; Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ | OID | DATE | ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables using INNER JOIN as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS INNER JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +----+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +----+----------+--------+---------------------+ | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
- 60. SQL - LEFT JOINSSQL - LEFT JOINS The SQL LEFT JOIN returns all rows from the left table, even if there are no matches in the right table. This means that if the ON clause matches 0 zero records in right table, the join will still return a row in the result, but with NULL in each column from right table. This means that a left join returns all the values from the left table, plus matched values from the right table or NULL in case of no matching join predicate. Syntax: The basic syntax of LEFT JOIN is as follows: SELECT table1.column1, table2.column2... FROM table1 LEFT JOIN table2 ON table1.common_field = table2.common_field; Here given condition could be any given expression based on your requirement. Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ | OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables using LEFT JOIN as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS LEFT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +----+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +----+----------+--------+---------------------+ | 1 | Ramesh | NULL | NULL | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 |
- 61. | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | | 5 | Hardik | NULL | NULL | | 6 | Komal | NULL | NULL | | 7 | Muffy | NULL | NULL | +----+----------+--------+---------------------+ Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 62. SQL - RIGHT JOINSSQL - RIGHT JOINS The SQL RIGHT JOIN returns all rows from the right table, even if there are no matches in the left table. This means that if the ON clause matches 0 zero records in left table, the join will still return a row in the result, but with NULL in each column from left table. This means that a right join returns all the values from the right table, plus matched values from the left table or NULL in case of no matching join predicate. Syntax: The basic syntax of RIGHT JOIN is as follows: SELECT table1.column1, table2.column2... FROM table1 RIGHT JOIN table2 ON table1.common_field = table2.common_field; Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables using RIGHT JOIN as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS RIGHT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +------+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +------+----------+--------+---------------------+ | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | +------+----------+--------+---------------------+
- 64. SQL - FULL JOINSSQL - FULL JOINS The SQL FULL JOIN combines the results of both left and right outer joins. The joined table will contain all records from both tables, and fill in NULLs for missing matches on either side. Syntax: The basic syntax of FULL JOIN is as follows: SELECT table1.column1, table2.column2... FROM table1 FULL JOIN table2 ON table1.common_field = table2.common_field; Here given condition could be any given expression based on your requirement. Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables using FULL JOIN as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS FULL JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +------+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +------+----------+--------+---------------------+ | 1 | Ramesh | NULL | NULL | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 |
- 65. | 5 | Hardik | NULL | NULL | | 6 | Komal | NULL | NULL | | 7 | Muffy | NULL | NULL | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | +------+----------+--------+---------------------+ If your Database does not support FULL JOIN like MySQL does not support FULL JOIN, then you can use UNION ALL clause to combine two JOINS as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS LEFT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID UNION ALL SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS RIGHT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 66. SQL - SELF JOINSSQL - SELF JOINS The SQL SELF JOIN is used to join a table to itself as if the table were two tables, temporarily renaming at least one table in the SQL statement. Syntax: The basic syntax of SELF JOIN is as follows: SELECT a.column_name, b.column_name... FROM table1 a, table1 b WHERE a.common_field = b.common_field; Here, WHERE clause could be any given expression based on your requirement. Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Now, let us join this table using SELF JOIN as follows: SQL> SELECT a.ID, b.NAME, a.SALARY FROM CUSTOMERS a, CUSTOMERS b WHERE a.SALARY < b.SALARY; This would produce the following result: +----+----------+---------+ | ID | NAME | SALARY | +----+----------+---------+ | 2 | Ramesh | 1500.00 | | 2 | kaushik | 1500.00 | | 1 | Chaitali | 2000.00 | | 2 | Chaitali | 1500.00 | | 3 | Chaitali | 2000.00 | | 6 | Chaitali | 4500.00 | | 1 | Hardik | 2000.00 | | 2 | Hardik | 1500.00 | | 3 | Hardik | 2000.00 | | 4 | Hardik | 6500.00 | | 6 | Hardik | 4500.00 | | 1 | Komal | 2000.00 | | 2 | Komal | 1500.00 | | 3 | Komal | 2000.00 | | 1 | Muffy | 2000.00 | | 2 | Muffy | 1500.00 | | 3 | Muffy | 2000.00 | | 4 | Muffy | 6500.00 | | 5 | Muffy | 8500.00 | | 6 | Muffy | 4500.00 |
- 68. SQL - CARTESIAN OR CROSS JOINSSQL - CARTESIAN OR CROSS JOINS The CARTESIAN JOIN or CROSS JOIN returns the Cartesian product of the sets of records from the two or more joined tables. Thus, it equates to an inner join where the join-condition always evaluates to True or where the join-condition is absent from the statement. Syntax: The basic syntax of CARTESIAN JOIN or CROSS JOIN is as follows: SELECT table1.column1, table2.column2... FROM table1, table2 [, table3 ] Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables using INNER JOIN as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS, ORDERS; This would produce the following result: +----+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +----+----------+--------+---------------------+ | 1 | Ramesh | 3000 | 2009-10-08 00:00:00 | | 1 | Ramesh | 1500 | 2009-10-08 00:00:00 | | 1 | Ramesh | 1560 | 2009-11-20 00:00:00 | | 1 | Ramesh | 2060 | 2008-05-20 00:00:00 | | 2 | Khilan | 3000 | 2009-10-08 00:00:00 | | 2 | Khilan | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 2 | Khilan | 2060 | 2008-05-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 3 | kaushik | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 2060 | 2008-05-20 00:00:00 |
- 69. | 4 | Chaitali | 3000 | 2009-10-08 00:00:00 | | 4 | Chaitali | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | | 5 | Hardik | 3000 | 2009-10-08 00:00:00 | | 5 | Hardik | 1500 | 2009-10-08 00:00:00 | | 5 | Hardik | 1560 | 2009-11-20 00:00:00 | | 5 | Hardik | 2060 | 2008-05-20 00:00:00 | | 6 | Komal | 3000 | 2009-10-08 00:00:00 | | 6 | Komal | 1500 | 2009-10-08 00:00:00 | | 6 | Komal | 1560 | 2009-11-20 00:00:00 | | 6 | Komal | 2060 | 2008-05-20 00:00:00 | | 7 | Muffy | 3000 | 2009-10-08 00:00:00 | | 7 | Muffy | 1500 | 2009-10-08 00:00:00 | | 7 | Muffy | 1560 | 2009-11-20 00:00:00 | | 7 | Muffy | 2060 | 2008-05-20 00:00:00 | +----+----------+--------+---------------------+ Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 70. SQL - UNIONS CLAUSESQL - UNIONS CLAUSE The SQL UNION clause/operator is used to combine the results of two or more SELECT statements without returning any duplicate rows. To use UNION, each SELECT must have the same number of columns selected, the same number of column expressions, the same data type, and have them in the same order, but they do not have to be the same length. Syntax: The basic syntax of UNION is as follows: SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition] UNION SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition] Here given condition could be any given expression based on your requirement. Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, let us join these two tables in our SELECT statement as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS LEFT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID UNION SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS RIGHT JOIN ORDERS
- 71. ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +------+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +------+----------+--------+---------------------+ | 1 | Ramesh | NULL | NULL | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | | 5 | Hardik | NULL | NULL | | 6 | Komal | NULL | NULL | | 7 | Muffy | NULL | NULL | +------+----------+--------+---------------------+ The UNION ALL Clause: The UNION ALL operator is used to combine the results of two SELECT statements including duplicate rows. The same rules that apply to UNION apply to the UNION ALL operator. Syntax: The basic syntax of UNION ALL is as follows: SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition] UNION ALL SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition] Here given condition could be any given expression based on your requirement. Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+
- 72. Now, let us join these two tables in our SELECT statement as follows: SQL> SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS LEFT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID UNION ALL SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS RIGHT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID; This would produce the following result: +------+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +------+----------+--------+---------------------+ | 1 | Ramesh | NULL | NULL | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | | 5 | Hardik | NULL | NULL | | 6 | Komal | NULL | NULL | | 7 | Muffy | NULL | NULL | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | +------+----------+--------+---------------------+ There are two other clauses i. e. , operators, which are very similar to UNION clause: SQL INTERSECT Clause: is used to combine two SELECT statements, but returns rows only from the first SELECT statement that are identical to a row in the second SELECT statement. SQL EXCEPT Clause : combines two SELECT statements and returns rows from the first SELECT statement that are not returned by the second SELECT statement. Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 73. SQL - NULL VALUESSQL - NULL VALUES The SQL NULL is the term used to represent a missing value. A NULL value in a table is a value in a field that appears to be blank. A field with a NULL value is a field with no value. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. Syntax: The basic syntax of NULL while creating a table: SQL> CREATE TABLE CUSTOMERS( ID INT NOT NULL, NAME VARCHAR (20) NOT NULL, AGE INT NOT NULL, ADDRESS CHAR (25) , SALARY DECIMAL (18, 2), PRIMARY KEY (ID) ); Here, NOT NULL signifies that column should always accept an explicit value of the given data type. There are two columns where we did not use NOT NULL, which means these columns could be NULL. A field with a NULL value is one that has been left blank during record creation. Example: The NULL value can cause problems when selecting data, however, because when comparing an unknown value to any other value, the result is always unknown and not included in the final results. You must use the IS NULL or IS NOT NULL operators in order to check for a NULL value. Consider the following table, CUSTOMERS having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | | | 7 | Muffy | 24 | Indore | | +----+----------+-----+-----------+----------+ Now, following is the usage of IS NOT NULL operator: SQL> SELECT ID, NAME, AGE, ADDRESS, SALARY FROM CUSTOMERS WHERE SALARY IS NOT NULL; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 |
- 74. | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | +----+----------+-----+-----------+----------+ Now, following is the usage of IS NULL operator: SQL> SELECT ID, NAME, AGE, ADDRESS, SALARY FROM CUSTOMERS WHERE SALARY IS NULL; This would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 6 | Komal | 22 | MP | | | 7 | Muffy | 24 | Indore | | +----+----------+-----+-----------+----------+
- 75. SQL - ALIAS SYNTAXSQL - ALIAS SYNTAX You can rename a table or a column temporarily by giving another name known as alias. The use of table aliases means to rename a table in a particular SQL statement. The renaming is a temporary change and the actual table name does not change in the database. The column aliases are used to rename a table's columns for the purpose of a particular SQL query. Syntax: The basic syntax of table alias is as follows: SELECT column1, column2.... FROM table_name AS alias_name WHERE [condition]; The basic syntax of column alias is as follows: SELECT column_name AS alias_name FROM table_name WHERE [condition]; Example: Consider the following two tables, a CUSTOMERS table is as follows: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ b Another table is ORDERS as follows: +-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+ Now, following is the usage of table alias: SQL> SELECT C.ID, C.NAME, C.AGE, O.AMOUNT FROM CUSTOMERS AS C, ORDERS AS O WHERE C.ID = O.CUSTOMER_ID; This would produce the following result: +----+----------+-----+--------+ | ID | NAME | AGE | AMOUNT |
- 76. +----+----------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Khilan | 25 | 1560 | | 4 | Chaitali | 25 | 2060 | +----+----------+-----+--------+ Following is the usage of column alias: SQL> SELECT ID AS CUSTOMER_ID, NAME AS CUSTOMER_NAME FROM CUSTOMERS WHERE SALARY IS NOT NULL; This would produce the following result: +-------------+---------------+ | CUSTOMER_ID | CUSTOMER_NAME | +-------------+---------------+ | 1 | Ramesh | | 2 | Khilan | | 3 | kaushik | | 4 | Chaitali | | 5 | Hardik | | 6 | Komal | | 7 | Muffy | +-------------+---------------+ Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 77. SQL - INDEXESSQL - INDEXES Indexes are special lookup tables that the database search engine can use to speed up data retrieval. Simply put, an index is a pointer to data in a table. An index in a database is very similar to an index in the back of a book. For example, if you want to reference all pages in a book that discuss a certain topic, you first refer to the index, which lists all topics alphabetically and are then referred to one or more specific page numbers. An index helps speed up SELECT queries and WHERE clauses, but it slows down data input, with UPDATE and INSERT statements. Indexes can be created or dropped with no effect on the data. Creating an index involves the CREATE INDEX statement, which allows you to name the index, to specify the table and which column or columns to index, and to indicate whether the index is in ascending or descending order. Indexes can also be unique, similar to the UNIQUE constraint, in that the index prevents duplicate entries in the column or combination of columns on which there's an index. The CREATE INDEX Command: The basic syntax of CREATE INDEX is as follows: CREATE INDEX index_name ON table_name; Single-Column Indexes: A single-column index is one that is created based on only one table column. The basic syntax is as follows: CREATE INDEX index_name ON table_name (column_name); Unique Indexes: Unique indexes are used not only for performance, but also for data integrity. A unique index does not allow any duplicate values to be inserted into the table. The basic syntax is as follows: CREATE UNIQUE INDEX index_name on table_name (column_name); Composite Indexes: A composite index is an index on two or more columns of a table. The basic syntax is as follows: CREATE INDEX index_name on table_name (column1, column2); Whether to create a single-column index or a composite index, take into consideration the column s that you may use very frequently in a query's WHERE clause as filter conditions. Should there be only one column used, a single-column index should be the choice. Should there be two or more columns that are frequently used in the WHERE clause as filters, the composite index would be the best choice. Implicit Indexes: Implicit indexes are indexes that are automatically created by the database server when an object is created. Indexes are automatically created for primary key constraints and unique constraints.
- 78. The DROP INDEX Command: An index can be dropped using SQL DROP command. Care should be taken when dropping an index because performance may be slowed or improved. The basic syntax is as follows: DROP INDEX index_name; You can check INDEX Constraint chapter to see actual examples on Indexes. When should indexes be avoided? Although indexes are intended to enhance a database's performance, there are times when they should be avoided. The following guidelines indicate when the use of an index should be reconsidered: Indexes should not be used on small tables. Tables that have frequent, large batch update or insert operations. Indexes should not be used on columns that contain a high number of NULL values. Columns that are frequently manipulated should not be indexed. Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 79. SQL - ALTER TABLE COMMANDSQL - ALTER TABLE COMMAND The SQL ALTER TABLE command is used to add, delete or modify columns in an existing table. You would also use ALTER TABLE command to add and drop various constraints on a an existing table. Syntax: The basic syntax of ALTER TABLE to add a new column in an existing table is as follows: ALTER TABLE table_name ADD column_name datatype; The basic syntax of ALTER TABLE to DROP COLUMN in an existing table is as follows: ALTER TABLE table_name DROP COLUMN column_name; The basic syntax of ALTER TABLE to change the DATA TYPE of a column in a table is as follows: ALTER TABLE table_name MODIFY COLUMN column_name datatype; The basic syntax of ALTER TABLE to add a NOT NULL constraint to a column in a table is as follows: ALTER TABLE table_name MODIFY column_name datatype NOT NULL; The basic syntax of ALTER TABLE to ADD UNIQUE CONSTRAINT to a table is as follows: ALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...); The basic syntax of ALTER TABLE to ADD CHECK CONSTRAINT to a table is as follows: ALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint CHECK (CONDITION); The basic syntax of ALTER TABLE to ADD PRIMARY KEY constraint to a table is as follows: ALTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...); The basic syntax of ALTER TABLE to DROP CONSTRAINT from a table is as follows: ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint; If you're using MySQL, the code is as follows: ALTER TABLE table_name DROP INDEX MyUniqueConstraint; The basic syntax of ALTER TABLE to DROP PRIMARY KEY constraint from a table is as follows: ALTER TABLE table_name DROP CONSTRAINT MyPrimaryKey; If you're using MySQL, the code is as follows:
- 80. ALTER TABLE table_name DROP PRIMARY KEY; Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is the example to ADD a new column in an existing table: ALTER TABLE CUSTOMERS ADD SEX char(1); Now, CUSTOMERS table is changed and following would be output from SELECT statement: +----+---------+-----+-----------+----------+------+ | ID | NAME | AGE | ADDRESS | SALARY | SEX | +----+---------+-----+-----------+----------+------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | NULL | | 2 | Ramesh | 25 | Delhi | 1500.00 | NULL | | 3 | kaushik | 23 | Kota | 2000.00 | NULL | | 4 | kaushik | 25 | Mumbai | 6500.00 | NULL | | 5 | Hardik | 27 | Bhopal | 8500.00 | NULL | | 6 | Komal | 22 | MP | 4500.00 | NULL | | 7 | Muffy | 24 | Indore | 10000.00 | NULL | +----+---------+-----+-----------+----------+------+ Following is the example to DROP sex column from existing table: ALTER TABLE CUSTOMERS DROP SEX; Now, CUSTOMERS table is changed and following would be output from SELECT statement: +----+---------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+---------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Ramesh | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | kaushik | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+---------+-----+-----------+----------+
- 81. SQL - TRUNCATE TABLE COMMANDSQL - TRUNCATE TABLE COMMAND The SQL TRUNCATE TABLE command is used to delete complete data from an existing table. You can also use DROP TABLE command to delete complete table but it would remove complete table structure form the database and you would need to re-create this table once again if you wish you store some data. Syntax: The basic syntax of TRUNCATE TABLE is as follows: TRUNCATE TABLE table_name; Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is the example to truncate: SQL > TRUNCATE TABLE CUSTOMERS; Now, CUSTOMERS table is truncated and following would be the output from SELECT statement: SQL> SELECT * FROM CUSTOMERS; Empty set (0.00 sec)
- 82. SQL - USING VIEWSSQL - USING VIEWS A view is nothing more than a SQL statement that is stored in the database with an associated name. A view is actually a composition of a table in the form of a predefined SQL query. A view can contain all rows of a table or select rows from a table. A view can be created from one or many tables which depends on the written SQL query to create a view. Views, which are kind of virtual tables, allow users to do the following: Structure data in a way that users or classes of users find natural or intuitive. Restrict access to the data such that a user can see and sometimes modify exactly what they need and no more. Summarize data from various tables which can be used to generate reports. Creating Views: Database views are created using the CREATE VIEW statement. Views can be created from a single table, multiple tables, or another view. To create a view, a user must have the appropriate system privilege according to the specific implementation. The basic CREATE VIEW syntax is as follows: CREATE VIEW view_name AS SELECT column1, column2..... FROM table_name WHERE [condition]; You can include multiple tables in your SELECT statement in very similar way as you use them in normal SQL SELECT query. Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Now, following is the example to create a view from CUSTOMERS table. This view would be used to have customer name and age from CUSTOMERS table: SQL > CREATE VIEW CUSTOMERS_VIEW AS SELECT name, age FROM CUSTOMERS; Now, you can query CUSTOMERS_VIEW in similar way as you query an actual table. Following is the example: SQL > SELECT * FROM CUSTOMERS_VIEW;
- 83. This would produce the following result: +----------+-----+ | name | age | +----------+-----+ | Ramesh | 32 | | Khilan | 25 | | kaushik | 23 | | Chaitali | 25 | | Hardik | 27 | | Komal | 22 | | Muffy | 24 | +----------+-----+ The WITH CHECK OPTION: The WITH CHECK OPTION is a CREATE VIEW statement option. The purpose of the WITH CHECK OPTION is to ensure that all UPDATE and INSERTs satisfy the conditions in the view definition. If they do not satisfy the conditions, the UPDATE or INSERT returns an error. The following is an example of creating same view CUSTOMERS_VIEW with the WITH CHECK OPTION: CREATE VIEW CUSTOMERS_VIEW AS SELECT name, age FROM CUSTOMERS WHERE age IS NOT NULL WITH CHECK OPTION; The WITH CHECK OPTION in this case should deny the entry of any NULL values in the view's AGE column, because the view is defined by data that does not have a NULL value in the AGE column. Updating a View: A view can be updated under certain conditions: The SELECT clause may not contain the keyword DISTINCT. The SELECT clause may not contain summary functions. The SELECT clause may not contain set functions. The SELECT clause may not contain set operators. The SELECT clause may not contain an ORDER BY clause. The FROM clause may not contain multiple tables. The WHERE clause may not contain subqueries. The query may not contain GROUP BY or HAVING. Calculated columns may not be updated. All NOT NULL columns from the base table must be included in the view in order for the INSERT query to function. So if a view satisfies all the above-mentioned rules then you can update a view. Following is an example to update the age of Ramesh: SQL > UPDATE CUSTOMERS_VIEW SET AGE = 35 WHERE name='Ramesh';
- 84. This would ultimately update the base table CUSTOMERS and same would reflect in the view itself. Now, try to query base table, and SELECT statement would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Inserting Rows into a View: Rows of data can be inserted into a view. The same rules that apply to the UPDATE command also apply to the INSERT command. Here we can not insert rows in CUSTOMERS_VIEW because we have not included all the NOT NULL columns in this view, otherwise you can insert rows in a view in similar way as you insert them in a table. Deleting Rows into a View: Rows of data can be deleted from a view. The same rules that apply to the UPDATE and INSERT commands apply to the DELETE command. Following is an example to delete a record having AGE= 22. SQL > DELETE FROM CUSTOMERS_VIEW WHERE age = 22; This would ultimately delete a row from the base table CUSTOMERS and same would reflect in the view itself. Now, try to query base table, and SELECT statement would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Dropping Views: Obviously, where you have a view, you need a way to drop the view if it is no longer needed. The syntax is very simple as given below: DROP VIEW view_name; Following is an example to drop CUSTOMERS_VIEW from CUSTOMERS table: DROP VIEW CUSTOMERS_VIEW; Loading [MathJax]/jax/output/HTML-CSS/jax.js
- 85. SQL - HAVING CLAUSESQL - HAVING CLAUSE The HAVING clause enables you to specify conditions that filter which group results appear in the final results. The WHERE clause places conditions on the selected columns, whereas the HAVING clause places conditions on groups created by the GROUP BY clause. Syntax: The following is the position of the HAVING clause in a query: SELECT FROM WHERE GROUP BY HAVING ORDER BY The HAVING clause must follow the GROUP BY clause in a query and must also precede the ORDER BY clause if used. The following is the syntax of the SELECT statement, including the HAVING clause: SELECT column1, column2 FROM table1, table2 WHERE [ conditions ] GROUP BY column1, column2 HAVING [ conditions ] ORDER BY column1, column2 Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is the example, which would display record for which similar age count would be more than or equal to 2: SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY FROM CUSTOMERS GROUP BY age HAVING COUNT(age) >= 2; This would produce the following result: +----+--------+-----+---------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+--------+-----+---------+---------+ | 2 | Khilan | 25 | Delhi | 1500.00 | +----+--------+-----+---------+---------+
- 87. SQL - TRANSACTIONSSQL - TRANSACTIONS A transaction is a unit of work that is performed against a database. Transactions are units or sequences of work accomplished in a logical order, whether in a manual fashion by a user or automatically by some sort of a database program. A transaction is the propagation of one or more changes to the database. For example, if you are creating a record or updating a record or deleting a record from the table, then you are performing transaction on the table. It is important to control transactions to ensure data integrity and to handle database errors. Practically, you will club many SQL queries into a group and you will execute all of them together as a part of a transaction. Properties of Transactions: Transactions have the following four standard properties, usually referred to by the acronym ACID: Atomicity: ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure, and previous operations are rolled back to their former state. Consistency: ensures that the database properly changes states upon a successfully committed transaction. Isolation: enables transactions to operate independently of and transparent to each other. Durability: ensures that the result or effect of a committed transaction persists in case of a system failure. Transaction Control: There are following commands used to control transactions: COMMIT: to save the changes. ROLLBACK: to rollback the changes. SAVEPOINT: creates points within groups of transactions in which to ROLLBACK SET TRANSACTION: Places a name on a transaction. Transactional control commands are only used with the DML commands INSERT, UPDATE and DELETE only. They can not be used while creating tables or dropping them because these operations are automatically commited in the database. The COMMIT Command: The COMMIT command is the transactional command used to save changes invoked by a transaction to the database. The COMMIT command saves all transactions to the database since the last COMMIT or ROLLBACK command. The syntax for COMMIT command is as follows: COMMIT; Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+
- 88. | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is the example which would delete records from the table having age = 25 and then COMMIT the changes in the database. SQL> DELETE FROM CUSTOMERS WHERE AGE = 25; SQL> COMMIT; As a result, two rows from the table would be deleted and SELECT statement would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ The ROLLBACK Command: The ROLLBACK command is the transactional command used to undo transactions that have not already been saved to the database. The ROLLBACK command can only be used to undo transactions since the last COMMIT or ROLLBACK command was issued. The syntax for ROLLBACK command is as follows: ROLLBACK; Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Following is the example, which would delete records from the table having age = 25 and then ROLLBACK the changes in the database. SQL> DELETE FROM CUSTOMERS WHERE AGE = 25; SQL> ROLLBACK;
- 89. As a result, delete operation would not impact the table and SELECT statement would produce the following result: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ The SAVEPOINT Command: A SAVEPOINT is a point in a transaction when you can roll the transaction back to a certain point without rolling back the entire transaction. The syntax for SAVEPOINT command is as follows: SAVEPOINT SAVEPOINT_NAME; This command serves only in the creation of a SAVEPOINT among transactional statements. The ROLLBACK command is used to undo a group of transactions. The syntax for rolling back to a SAVEPOINT is as follows: ROLLBACK TO SAVEPOINT_NAME; Following is an example where you plan to delete the three different records from the CUSTOMERS table. You want to create a SAVEPOINT before each delete, so that you can ROLLBACK to any SAVEPOINT at any time to return the appropriate data to its original state: Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Now, here is the series of operations: SQL> SAVEPOINT SP1; Savepoint created. SQL> DELETE FROM CUSTOMERS WHERE ID=1; 1 row deleted. SQL> SAVEPOINT SP2; Savepoint created. SQL> DELETE FROM CUSTOMERS WHERE ID=2; 1 row deleted. SQL> SAVEPOINT SP3; Savepoint created. SQL> DELETE FROM CUSTOMERS WHERE ID=3;
- 90. 1 row deleted. Now that the three deletions have taken place, say you have changed your mind and decided to ROLLBACK to the SAVEPOINT that you identified as SP2. Because SP2 was created after the first deletion, the last two deletions are undone: SQL> ROLLBACK TO SP2; Rollback complete. Notice that only the first deletion took place since you rolled back to SP2: SQL> SELECT * FROM CUSTOMERS; +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ 6 rows selected. The RELEASE SAVEPOINT Command: The RELEASE SAVEPOINT command is used to remove a SAVEPOINT that you have created. The syntax for RELEASE SAVEPOINT is as follows: RELEASE SAVEPOINT SAVEPOINT_NAME; Once a SAVEPOINT has been released, you can no longer use the ROLLBACK command to undo transactions performed since the SAVEPOINT. The SET TRANSACTION Command: The SET TRANSACTION command can be used to initiate a database transaction. This command is used to specify characteristics for the transaction that follows. For example, you can specify a transaction to be read only, or read write. The syntax for SET TRANSACTION is as follows: SET TRANSACTION [ READ WRITE | READ ONLY ];
- 91. SQL - SUB QUERIESSQL - SUB QUERIES A Subquery or Inner query or Nested query is a query within another SQL query and embedded within the WHERE clause. A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved. Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN etc. There are a few rules that subqueries must follow: Subqueries must be enclosed within parentheses. A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns. An ORDER BY cannot be used in a subquery, although the main query can use an ORDER BY. The GROUP BY can be used to perform the same function as the ORDER BY in a subquery. Subqueries that return more than one row can only be used with multiple value operators, such as the IN operator. The SELECT list cannot include any references to values that evaluate to a BLOB, ARRAY, CLOB, or NCLOB. A subquery cannot be immediately enclosed in a set function. The BETWEEN operator cannot be used with a subquery; however, the BETWEEN operator can be used within the subquery. Subqueries with the SELECT Statement: Subqueries are most frequently used with the SELECT statement. The basic syntax is as follows: SELECT column_name [, column_name ] FROM table1 [, table2 ] WHERE column_name OPERATOR (SELECT column_name [, column_name ] FROM table1 [, table2 ] [WHERE]) Example: Consider the CUSTOMERS table having the following records: +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Now, let us check following subquery with SELECT statement: SQL> SELECT * FROM CUSTOMERS
- 92. WHERE ID IN (SELECT ID FROM CUSTOMERS WHERE SALARY > 4500) ; This would produce the following result: +----+----------+-----+---------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+---------+----------+ | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+---------+----------+ Subqueries with the INSERT Statement: Subqueries also can be used with INSERT statements. The INSERT statement uses the data returned from the subquery to insert into another table. The selected data in the subquery can be modified with any of the character, date or number functions. The basic syntax is as follows: INSERT INTO table_name [ (column1 [, column2 ]) ] SELECT [ *|column1 [, column2 ] FROM table1 [, table2 ] [ WHERE VALUE OPERATOR ] Example: Consider a table CUSTOMERS_BKP with similar structure as CUSTOMERS table. Now to copy complete CUSTOMERS table into CUSTOMERS_BKP, following is the syntax: SQL> INSERT INTO CUSTOMERS_BKP SELECT * FROM CUSTOMERS WHERE ID IN (SELECT ID FROM CUSTOMERS) ; Subqueries with the UPDATE Statement: The subquery can be used in conjunction with the UPDATE statement. Either single or multiple columns in a table can be updated when using a subquery with the UPDATE statement. The basic syntax is as follows: UPDATE table SET column_name = new_value [ WHERE OPERATOR [ VALUE ] (SELECT COLUMN_NAME FROM TABLE_NAME) [ WHERE) ] Example: Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table. Following example updates SALARY by 0.25 times in CUSTOMERS table for all the customers whose AGE is greater than or equal to 27: SQL> UPDATE CUSTOMERS SET SALARY = SALARY * 0.25 WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE >= 27 ); This would impact two rows and finally CUSTOMERS table would have the following records:
- 93. +----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 35 | Ahmedabad | 125.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 2125.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+ Subqueries with the DELETE Statement: The subquery can be used in conjunction with the DELETE statement like with any other statements mentioned above. The basic syntax is as follows: DELETE FROM TABLE_NAME [ WHERE OPERATOR [ VALUE ] (SELECT COLUMN_NAME FROM TABLE_NAME) [ WHERE) ] Example: Assuming, we have CUSTOMERS_BKP table available which is backup of CUSTOMERS table. Following example deletes records from CUSTOMERS table for all the customers whose AGE is greater than or equal to 27: SQL> DELETE FROM CUSTOMERS WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP WHERE AGE > 27 ); This would impact two rows and finally CUSTOMERS table would have the following records: +----+----------+-----+---------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+---------+----------+ | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+---------+----------+
- 94. SQL - USING SEQUENCESSQL - USING SEQUENCES A sequence is a set of integers 1, 2, 3, ... that are generated in order on demand. Sequences are frequently used in databases because many applications require each row in a table to contain a unique value, and sequences provide an easy way to generate them. This chapter describes how to use sequences in MySQL. Using AUTO_INCREMENT column: The simplest way in MySQL to use sequences is to define a column as AUTO_INCREMENT and leave rest of the things to MySQL to take care. Example: Try out the following example. This will create table and after that it will insert few rows in this table where it is not required to give record ID because its auto-incremented by MySQL. mysql> CREATE TABLE INSECT -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected ); Query OK, 0 rows affected (0.02 sec) mysql> INSERT INTO INSECT (id,name,date,origin) VALUES -> (NULL,'housefly','2001-09-10','kitchen'), -> (NULL,'millipede','2001-09-10','driveway'), -> (NULL,'grasshopper','2001-09-10','front yard'); Query OK, 3 rows affected (0.02 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql> SELECT * FROM INSECT ORDER BY id; +----+-------------+------------+------------+ | id | name | date | origin | +----+-------------+------------+------------+ | 1 | housefly | 2001-09-10 | kitchen | | 2 | millipede | 2001-09-10 | driveway | | 3 | grasshopper | 2001-09-10 | front yard | +----+-------------+------------+------------+ 3 rows in set (0.00 sec) Obtain AUTO_INCREMENT Values: LAST_INSERT_ID is a SQL function, so you can use it from within any client that understands how to issue SQL statements. Otherwise PERL and PHP scripts provide exclusive functions to retrieve auto- incremented value of last record. PERL Example: Use the mysql_insertid attribute to obtain the AUTO_INCREMENT value generated by a query. This attribute is accessed through either a database handle or a statement handle, depending on how you issue the query. The following example references it through the database handle: $dbh->do ("INSERT INTO INSECT (name,date,origin) VALUES('moth','2001-09-14','windowsill')"); my $seq = $dbh->{mysql_insertid}; PHP Example: After issuing a query that generates an AUTO_INCREMENT value, retrieve the value by calling
- 95. mysql_insert_id: mysql_query ("INSERT INTO INSECT (name,date,origin) VALUES('moth','2001-09-14','windowsill')", $conn_id); $seq = mysql_insert_id ($conn_id); Renumbering an Existing Sequence: There may be a case when you have deleted many records from a table and you want to resequence all the records. This can be done by using a simple trick but you should be very careful to do so if your table is having join, with other table. If you determine that resequencing an AUTO_INCREMENT column is unavoidable, the way to do it is to drop the column from the table, then add it again. The following example shows how to renumber the id values in the insect table using this technique: mysql> ALTER TABLE INSECT DROP id; mysql> ALTER TABLE insect -> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST, -> ADD PRIMARY KEY (id); Starting a Sequence at a Particular Value: By default, MySQL will start sequence from 1 but you can specify any other number as well at the time of table creation. Following is the example where MySQL will start sequence from 100. mysql> CREATE TABLE INSECT -> ( -> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100, -> PRIMARY KEY (id), -> name VARCHAR(30) NOT NULL, # type of insect -> date DATE NOT NULL, # date collected -> origin VARCHAR(30) NOT NULL # where collected ); Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE. mysql> ALTER TABLE t AUTO_INCREMENT = 100; Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js
- 96. SQL - CLONE TABLESSQL - CLONE TABLES There may be a situation when you need an exact copy of a table and CREATE TABLE ... SELECT... doesn't suit your purposes because the copy must include the same indexes, default values, and so forth. If you are using MySQL RDBMS, you can handle this situation by the following steps: Use SHOW CREATE TABLE command to get a CREATE TABLE statement that specifies the source table's structure, indexes and all. Modify the statement to change the table name to that of the clone table and execute the statement. This way you will have exact clone table. Optionally, if you need the table contents copied as well, issue an INSERT INTO ... SELECT statement, too. Example: Try out the following example to create a clone table for TUTORIALS_TBL whose structure is as follows: Step 1: Get complete structure about table. SQL> SHOW CREATE TABLE TUTORIALS_TBL G; *************************** 1. row *************************** Table: TUTORIALS_TBL Create Table: CREATE TABLE `TUTORIALS_TBL` ( `tutorial_id` int(11) NOT NULL auto_increment, `tutorial_title` varchar(100) NOT NULL default '', `tutorial_author` varchar(40) NOT NULL default '', `submission_date` date default NULL, PRIMARY KEY (`tutorial_id`), UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) ) TYPE=MyISAM 1 row in set (0.00 sec) Step 2: Rename this table and create another table. SQL> CREATE TABLE `CLONE_TBL` ( -> `tutorial_id` int(11) NOT NULL auto_increment, -> `tutorial_title` varchar(100) NOT NULL default '', -> `tutorial_author` varchar(40) NOT NULL default '', -> `submission_date` date default NULL, -> PRIMARY KEY (`tutorial_id`), -> UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`) -> ) TYPE=MyISAM; Query OK, 0 rows affected (1.80 sec) Step 3: After executing step 2, you will clone a table in your database. If you want to copy data from old table, then you can do it by using INSERT INTO... SELECT statement. SQL> INSERT INTO CLONE_TBL (tutorial_id, -> tutorial_title, -> tutorial_author, -> submission_date)
- 97. -> SELECT tutorial_id,tutorial_title, -> tutorial_author,submission_date, -> FROM TUTORIALS_TBL; Query OK, 3 rows affected (0.07 sec) Records: 3 Duplicates: 0 Warnings: 0 Finally, you will have exact clone table as you wanted to have.
- 98. SQL - TEMPORARY TABLESSQL - TEMPORARY TABLES There are RDBMS, which support temporary tables. Temporary Tables are a great feature that lets you store and process intermediate results by using the same selection, update, and join capabilities that you can use with typical SQL Server tables. The temporary tables could be very useful in some cases to keep temporary data. The most important thing that should be known for temporary tables is that they will be deleted when the current client session terminates. Temporary tables are available in MySQL version 3.23 onwards. If you use an older version of MySQL than 3.23, you can't use temporary tables, but you can use heap tables. As stated earlier, temporary tables will only last as long as the session is alive. If you run the code in a PHP script, the temporary table will be destroyed automatically when the script finishes executing. If you are connected to the MySQL database server through the MySQL client program, then the temporary table will exist until you close the client or manually destroy the table. Example: Here is an example showing you usage of temporary table: mysql> CREATE TEMPORARY TABLE SALESSUMMARY ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec) mysql> INSERT INTO SALESSUMMARY -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SALESSUMMARY; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec) When you issue a SHOW TABLES command, then your temporary table would not be listed out in the list. Now if you will log out of the MySQL session and then you will issue a SELECT command, then you will find no data available in the database. Even your temporary table would also not exist. Dropping Temporary Tables: By default, all the temporary tables are deleted by MySQL when your database connection gets terminated. Still you want to delete them in between, then you do so by issuing DROP TABLE command. Following is the example on dropping a temporary table. mysql> CREATE TEMPORARY TABLE SALESSUMMARY ( -> product_name VARCHAR(50) NOT NULL -> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00 -> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00 -> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0 ); Query OK, 0 rows affected (0.00 sec)
- 99. mysql> INSERT INTO SALESSUMMARY -> (product_name, total_sales, avg_unit_price, total_units_sold) -> VALUES -> ('cucumber', 100.25, 90, 2); mysql> SELECT * FROM SALESSUMMARY; +--------------+-------------+----------------+------------------+ | product_name | total_sales | avg_unit_price | total_units_sold | +--------------+-------------+----------------+------------------+ | cucumber | 100.25 | 90.00 | 2 | +--------------+-------------+----------------+------------------+ 1 row in set (0.00 sec) mysql> DROP TABLE SALESSUMMARY; mysql> SELECT * FROM SALESSUMMARY; ERROR 1146: Table 'TUTORIALS.SALESSUMMARY' doesn't exist
- 100. SQL - INJECTIONSQL - INJECTION If you take user input through a webpage and insert it into a SQL database, there's a chance that you have left yourself wide open for a security issue known as SQL Injection. This lesson will teach you how to help prevent this from happening and help you secure your scripts and SQL statements in your server side scripts such as PERL Script. Injection usually occurs when you ask a user for input, like their name, and instead of a name they give you a SQL statement that you will unknowingly run on your database. Never trust user provided data, process this data only after validation; as a rule, this is done by pattern matching. In the example below, the name is restricted to alphanumerical chars plus underscore and to a length between 8 and 20 chars modifytheserulesasneeded. if (preg_match("/^w{8,20}$/", $_GET['username'], $matches)) { $result = mysql_query("SELECT * FROM CUSTOMERS WHERE name=$matches[0]"); } else { echo "user name not accepted"; } To demonstrate the problem, consider this excerpt: // supposed input $name = "Qadir'; DELETE FROM CUSTOMERS;"; mysql_query("SELECT * FROM CUSTOMSRS WHERE name='{$name}'"); The function call is supposed to retrieve a record from the CUSTOMERS table where the name column matches the name specified by the user. Under normal circumstances, namewouldonlycontainalphanumericcharactersandperhapsspaces, suchasthestringilia. Buthere, byappendinganentirelynewqueryto name, the call to the database turns into disaster: the injected DELETE query removes all records from CUSTOMERS. Fortunately, if you use MySQL, the mysql_query function does not permit query stacking or executing multiple SQL queries in a single function call. If you try to stack queries, the call fails. However, other PHP database extensions, such as SQLite and PostgreSQL, happily perform stacked queries, executing all of the queries provided in one string and creating a serious security problem. Preventing SQL Injection: You can handle all escape characters smartly in scripting languages like PERL and PHP. The MySQL extension for PHP provides the function mysql_real_escape_string to escape input characters that are special to MySQL. if (get_magic_quotes_gpc()) { $name = stripslashes($name); } $name = mysql_real_escape_string($name); mysql_query("SELECT * FROM CUSTOMERS WHERE name='{$name}'"); The LIKE Quandary: To address the LIKE quandary, a custom escaping mechanism must convert user-supplied '%' and '_' characters to literals. Use addcslashes, a function that let's you specify a character range to escape.
- 101. $sub = addcslashes(mysql_real_escape_string("%str"), "%_"); // $sub == %str_ mysql_query("SELECT * FROM messages WHERE subject LIKE '{$sub}%'"); Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js