STRUCTURED QUERY LANGUAGE

DATABASE SYSTEMS
STAFF NAME : D.SARITHA
ASSISTANT PROFESSOR
DEPARTMENT OF COMPUTER APPLICATIONS
BON SECOURS COLLEGE FOR WOMEN
THANJAVUR
UNIT : III
CHAPTER : 3
TOPIC : SQL

• Structure Query Language(SQL) is a database
query language used for storing and
managing data in Relational DBMS.
• SQL was the first commercial language
introduced for E.F Codd's Relational model of
database.
• Today almost all RDBMS(MySql, Oracle,
Infomix, Sybase, MS Access) use SQL as the
standard database query language.
• SQL is used to perform all types of data
operations in RDBMS.
INTRODUCTION TO SQL

• This includes changes to the structure of the table like
creation of table, altering table, deleting a table etc.
• All DDL commands are auto-committed. That means it
saves all the changes permanently in the database.
DDL: DATA DEFINITION LANGUAGE
Command Description
create to create new table or
database
alter for alteration
truncate delete data from table
drop to drop a table
rename to rename a table

• DML commands are used for manipulating the data stored
in the table and not the table itself.
• DML commands are not auto-committed. It means changes
are not permanent to database, they can be rolled back.
DML: DATA MANIPULATION LANGUAGE
Command Description
insert to insert a new row
update to update existing row
delete to delete a row
merge merging two rows or two
tables

These commands are to keep a check on other commands
and their affect on the database.
It can also make any temporary change permanent.
TCL: TRANSACTION CONTROL LANGUAGE
Command Description
commit to permanently save
rollback to undo change
savepoint to save temporarily

Data control language are the commands to grant and take
back authority from any database user.
DCL: DATA CONTROL LANGUAGE
Command Description
grant grant permission of
right
revoke take back permission.

Data query language is used to fetch data from tables based
on conditions that we can easily apply.
DQL: DATA QUERY LANGUAGE
Command Description
select retrieve records from
one or more table

Data Definition Language
SQL: CREATE COMMAND
create is a DDL SQL command used to create a table
or a database in relational database management
system.
CREATE DATABASE <DB_NAME>;
Creating a Database
To create a database in RDBMS, create command is used.
Following is the syntax,
CREATE DATABASE Test;

Creating a Table
create command can also be used to create
tables
CREATE TABLE <TABLE_NAME> ( column_name1
datatype1, column_name2 datatype2,
column_name3 datatype3, column_name4
datatype4 );
CREATE TABLE Student( student_id INT,
name VARCHAR(100), age INT);

Most commonly used datatypes for Table columns
Datatype Use
INT used for columns which will store integer values.
FLOAT used for columns which will store float values.
DOUBLE used for columns which will store float values.
VARCHAR used for columns which will be used to store characters
and integers, basically a string.
CHAR used for columns which will store char values(single
character).
DATE used for columns which will store date values.
TEXT used for columns which will store text which is generally
long in length.
Here we have listed some of the most commonly used datatypes used
for columns in tables.

alter command is used for altering the table structure, such as,
•to add a column to existing table
•to rename any existing column
•to change datatype of any column or to modify its size.
•to drop a column from the table.
SQL: ALTER command
ALTER TABLE table_name ADD( column_name datatype);
ALTER TABLE student ADD( address VARCHAR(200) );
ALTER TABLE table_name modify( column_name datatype );
Add a column
Modify an existing Column
ALTER TABLE student MODIFY( address varchar(300));

Rename a Column
ALTER TABLE table_name RENAME old_column_name TO
new_column_name;
ALTER TABLE student RENAME address TO location;
Drop a Column
ALTER TABLE table_name DROP( column_name);
ALTER TABLE student DROP( address);

TRUNCATE command removes all the records from a table. But this command
will not destroy the table's structure.
TRUNCATE COMMAND
TRUNCATE TABLE table_name
TRUNCATE TABLE student;
DROP command completely removes a table from the database. This
command will also destroy the table structure and the data stored in it.
DROP COMMAND
DROP TABLE table_name
DROP TABLE student;

RENAME command is used to set a new name for any
existing table.
RENAME QUERY
RENAME TABLE old_table_name to
new_table_name
RENAME TABLE student to students_info;

Insert command is used to insert data into a table
DATA MANIPULATION LANGUAGE
INSERT COMMAND
INSERT INTO table_name VALUES(data1, data2, ...)
INSERT INTO student VALUES(101, 'Adam', 15);
UPDATE command is used to update any record of data in a table
UPDATE COMMAND
UPDATE table_name SET column_name = new_value WHERE
some_condition;
UPDATE student SET age=18 WHERE student_id=102;

DELETE command is used to delete data from a table.
DELETE COMMAND
DELETE FROM student WHERE s_id=103;
TRANSACTION CONTROL LANGUAGE(TCL) COMMANDS
Transaction Control Language(TCL) commands are used to manage
transactions in the database.
COMMIT command is used to permanently save any transaction into the
database.
COMMIT command
COMMIT;

This command restores the database to last commited state.
It is also used with SAVEPOINT command to jump to a savepoint in an
ongoing transaction.
ROLLBACK COMMAND
ROLLBACK TO savepoint_name;
SAVEPOINT command is used to temporarily save a transaction so that you can
rollback to that point whenever required.
SAVEPOINT COMMAND
SAVEPOINT savepoint_name;
INSERT INTO class VALUES(5, 'Rahul');
COMMIT;
UPDATE class SET name = 'Abhijit' WHERE id = '5';
SAVEPOINT A;
INSERT INTO class VALUES(6, 'Chris');
SAVEPOINT B;
INSERT INTO class VALUES(7, 'Bravo');
SAVEPOINT C;
SELECT * FROM class;

Using GRANT and REVOKE
Data Control Language(DCL) is used to control privileges in
Database.
Privileges are of two types,
System:
This includes permissions for creating session, table, etc and
all types of other system privileges.
Object:
This includes permissions for any command or query to
perform any operation on the database tables.
DCL Commands
GRANT: Used to provide any user access privileges or other
privileges for the database.
REVOKE: Used to take back permissions from any user.

Allow a User to create session
Not even allowed to login and create a session until and unless proper
permissions/privileges are granted to the user
GRANT CREATE SESSION TO username;
Granting Privileges
To allow a user to create tables in the database, we can use the below
command
GRANT CREATE TABLE TO username;
GRANT CREATE SESSION TO Bob;
GRANT CREATE TABLE TO Bob;
GRANT SELECT ON DEPARTMENT TO BOB;
GRANT UPDATE(BUDGET) ON DEPARTMENT TO BOB,ALLEN;

Grant permission to create any table
we can grant privileges to a user to create any table using the below
command,
GRANT CREATE ANY TABLE TO username
GRANT CREATE ANY TABLE TO ALLEN
Grant permission to drop any table
GRANT DROP ANY TABLE TO username
GRANT DROP ANY TABLE TO ALLEN

Roles
Authorization granted to individual users.
CREATE ROLE INSTRUCTOR;
GRANT SELECT ON TAKES TO INSTRUCTOR;
CREATE ROLE DEAN;
GRANT DEAN TO AMIT;
GRANT INSTRUCTOR TO DEAN
Authorization on views
To allow a user to create views in the database, we can use the below
command
CREATE VIEW Geo-instructor as (Select * from instructor
where dept-name = ‘Geology’;
Select * from Geo-Instructor;

GRANT REFERENCES(DEPT-NAME) ON DEPARTMENT TO MARINO;
GRANT SELECT ON DEPARTMENT TO BOB WITH GRANT OPTION;
Authorizations on schema
To allow a user to refer the keys in the tables, we can use the below
command
Transfer of Privileges
To allow a user to pass the information to other users in the database,
we can use the below command
To take back Permissions
REVOKE CREATE TABLE FROM username
REVOKE CREATE TABLE FROM ALLEN
REVOKE SELECT ON DEPARTMENT FROM AMIT, SATOSHI RESTRICT;

DQL: DATA QUERY LANGUAGE
SELECT statement to display data of the table, based on a condition.
s_id name age address
101 Adam 15 Chennai
102 Alex 18 Delhi
103 Abhi 17 Banglore
104 Ankit 22 Mumbai
Using WHERE Clause
Consider a table student,
SELECT s_id, name, age, address FROM student WHERE s_id = 101;
101 Adam 15 chennai

SELECT s_id, name, age, address FROM student WHERE age between
15 and 18;
Using Between operator
SELECT s_id, name, age, address FROM student WHERE age >= 15
and <= 20;
Using Comparision operator
101 Adam 15 Chennai
102 Alex 18 Delhi

Using String Operations
LIKE clause compares data with an expression using wildcard operators to
match pattern given in the condition.
Wildcard operators
There are two wildcard operators that are used in LIKE clause.
• Percent sign %: represents zero, one or more than one character.
• Underscore sign _: represents only a single character.
SELECT * FROM Student WHERE name LIKE 'A%';
101 Adam 15 Chennai
102 Alex 18 Delhi
104 Ankit 22 Mumbai

SELECT * FROM Student WHERE name LIKE '_d%';
101 Adam 15 chennai
SELECT * FROM Student WHERE name LIKE '%x';
102 Alex 18 Delhi
Using Escape Character ()
SELECT * FROM Student WHERE name LIKE ‘an%it';
104 Ankit 22 Mumbai

Order by clause is used with SELECT statement for arranging retrieved data in
sorted order.
ORDER BY Clause
SELECT column-list|* FROM table-name ORDER BY ASC | DESC;
Syntax of Order By
eid name age salary
401 Anu 22 9000
402 Shane 29 8000
403 Rohan 34 6000
404 Scott 44 10000
405 Tiger 35 8000
Consider the following Emp table,

SELECT * FROM Emp ORDER BY salary;
eid name age salary
403 Rohan 34 6000
402 Shane 29 8000
405 Tiger 35 8000
401 Anu 22 9000
404 Scott 44 10000
SELECT * FROM Emp ORDER BY age desc;
eid name age salary
404 Scott 44 10000
405 Tiger 35 8000
403 Rohan 34 6000
402 Shane 29 8000
401 Anu 22 9000

Group by clause is used to group the results of a SELECT query
based on one or more columns.
Group By Clause
SELECT column_name, function(column_name) FROM
table_name WHERE condition GROUP BY column_name
SELECT name, age FROM Emp GROUP BY salary
Syntax
Example

STRUCTURED QUERY LANGUAGE

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