DBMS and SQL(structured query language) .pptx

Database
Database is collection of data in a format that can be easily accessed (Digital)
A software application used to manage our DB is called DBMS (Database Management System)

Types of Databases
Relational
Data stored in tables
Non-relational (NoSQL)
data not stored in tables
** We use SQL to work with relational DBMS

What is SQL?
Structured Query Language
SQL is a programming language used to interact with relational databases.
It is used to perform CRUD operations :
Create
Read
Update
Delete

Database Structure
Database
Table 1
Data
Table 2
Data

What is a table?
Student table

CREATE DATABASE db_name;
DROP DATABASE db_name;
Creating our First Database
Our first SQL Query

Creating our First Table
USE db_name;
CREATE TABLE table_name (
column_name1 datatype constraint,
column_name2 datatype constraint
);

SQL Datatypes
They define the type of values that can be stored in a column

SQL Datatypes
Signed & Unsigned
TINYINT UNSIGNED (0 to 255)
TINYINT (-128 to 127)

Typesof SQLCommands
DDL (Data Definition Language) : create, alter, rename, truncate & drop
DQL(Data Query Language) : select
DML (Data Manipulation Language) : select, insert, update & delete
DCL (Data Control Language) : grant & revoke permission to users
TCL (Transaction Control Language) : start transaction, commit, rollback etc.

Database related Queries
SHOW DATABASES;
SHOW TABLES;
CREATE DATABASE db_name;
CREATE DATABASE IF NOT EXISTS db_name;
DROP DATABASE db_name;
DROP DATABASE IF EXISTS db_name;

Table related Queries
Create
CREATE TABLE table_name (
);

SELECT * FROM table_name;
Select & ViewALLcolumns

Insert
INSERT INTO table_name
(colname1, colname2);
VALUES
(col1_v1, col2_v1),
(col1_v2, col2_v2);

Keys
Primary Key
It is a column (or set of columns) in a table that uniquely identifies each row. (a unique id)
There is only 1 PK & it should be NOT null.
Foreign Key
A foreign key is a column (or set of columns) in a table that refers to the primary key in another table.
There can be multiple FKs.
FKs can have duplicate & null values.

Keys
table1 - Student table2 - City

Constraints
UNIQUE
PRIMARY KEY
SQL constraints are used to specify rules for data in a table.
NOT NULL columns cannot have a null value
all values in column are different
makes a column unique & not null but used only for one

Constraints
FOREIGN KEY prevent actions that would destroy links between tables
DEFAULT sets the default value of a column

Constraints
CHECK it can limit the values allowed in a column

Create this sample table Insert this data

Select in Detail
used to select any data from the database
Basic Syntax
SELECT col1, col2 FROM table_name;
To Select ALL
SELECT * FROM table_name;

Where Clause
To define some conditions
SELECT col1, col2 FROM table_name
WHERE conditions;

Arithmetic Operators : +(addition) , -(subtraction), *(multiplication), /(division), %(modulus)
Comparison Operators : = (equal to), != (not equal to), > , >=, <, <=
Logical Operators : AND, OR , NOT, IN, BETWEEN, ALL, LIKE, ANY
Bitwise Operators: & (Bitwise AND), | (Bitwise OR)
Where Clause
UsingOperatorsin WHERE

Operators
AND (to check for both conditionsto be true)
OR (to check for one of the conditions to be true)

Between (selects for a given range)
In (matches any value in the list)
NOT (to negate the given condition)
Operators

Limit Clause
Sets an upper limit on number of (tuples)rows to be returned
LIMIT number;

Order By Clause
To sort in ascending (ASC)or descending order (DESC)
ORDER BY col_name(s) ASC;

Aggregate Functions
Aggregare functions perform a calculation on a set of values, and return a single value.
COUNT( )
MAX( )
MIN( )
SUM( )
AVG()
Get Average marks
Get Maximum Marks

Group By Clause
Groups rows that have the same values into summary rows.
It collects data from multiple records and groups the result by one or more column.
*Generally we use group by with some aggregation function.
Count number of students in each city

HavingClause
Similar to Where i.e. applies some condition on rows.
Used when we want to apply any condition after grouping.
Count number of students in each city where max marks cross 90.

General Order
SELECT column(s)
FROM table_name
WHERE condition
GROUPBY column(s)
HAVING condition
ORDERBY column(s) ASC;

Update (to update existingrows)
UPDATE table_name
SET col1 = val1, col2 = val2
WHERE condition;

Delete (to delete existing rows)
DELETE FROM table_name
WHERE condition;

Cascading for FK
On Delete Cascade
When we create a foreign key using this option, it deletes the referencing rows in the child table
when the referenced row is deleted in the parent table which has a primary key.
On Update Cascade
When we create a foreign key using UPDATE CASCADE the referencing rows are updated in the child
table when the referenced row is updated in the parent table which has a primary key.

Alter (to change the schema)
ADD Column
ALTER TABLE table_name
ADD COLUMN column_name datatype constraint;
DROP Column
DROP COLUMN column_name;
RENAME Table
RENAME TO new_table_name;

MODIFY Column (modify datatype/ constraint)
MODIFY col_name new_datatype new_constraint;
CHANGE Column (rename)
CHANGE COLUMN old_name new_name new_datatype new_constraint;

ADD Column
RENAME Table
DROP Column
MODIFY Column
CHANGE Column (rename)

Truncate (to delete table's data)
TRUNCATE TABLE table_name ;

Joins in SQL
Join is used to combine rows from two or more tables, based on a related column between them.

Types of Joins
Inner Join Left Join Right Join Full Join
Outer Joins

Inner Join
Returns records that have matching values in both tables
Syntax
SELECT column(s)
FROM tableA
INNER JOIN tableB
ON tableA.col_name = tableB.col_name;

Inner Join
Example
SELECT *
FROM student
INNER JOIN course
ON student.student_id = course.student_id;
student course
Result

Left Join
Returns all records from the left table, and the matched records from
the right table
Syntax
SELECT column(s)
FROM tableA
LEFT JOIN tableB

Left Join
Example
SELECT *
FROM student as s
LEFT JOIN course as c
ON s.student_id = c.student_id;
student course
Result

Right Join
Returns all records from the right table, and the matched records
from the left table
Syntax
SELECT column(s)
FROM tableA
RIGHT JOIN tableB

Right Join
Example
SELECT *
FROM student as s
RIGHT JOIN course as c
ON s.student_id = c.student_id;
student course
Result

Full Join
Returns all records when there is a match in either left or right table
Syntax in MySQL
LEFT JOIN
UNION
RIGHT JOIN

Full Join
Example
student
course
Result

Qs: Write SQL commands to display the right exclusive join :
Think & Ans
Right Exclusive Join
Left Exclusive Join

Self Join
It is a regular join but the table is joined with itself.
Syntax
SELECT column(s)
FROM table as a
JOIN table as b
ON a.col_name = b.col_name;

Self Join
Example
Employee
Result

Union
It isused to combine the result-set of two or more SELECTstatements.
GivesUNIQUE records.
Syntax
SELECT column(s) FROM tableA
UNION
SELECT column(s) FROM tableB
To use it :
every SELECT should have same no. of columns
columnsmust have similar data types
columns in every SELECT should be in same order

SQLSub Queries
A Subquery or Inner query or a Nested query is a query within another SQL query.
Query
Sub Query
It involves2 select statements.
Syntax
SELECT column(s)
FROM table_name
WHERE col_name operator
( subquery );

SQL Sub Queries
Example
Get names of all students who scored more than class average.
Step 1. Find the avg of class
Step 2. Find the names of students with marks > avg

SQL Sub Queries
Example
Find the names of all students with even roll numbers.
Step 1. Find the even roll numbers
Step 2. Find the names of students with even roll no

SQL Sub Queries
Example with FROM
Find the max marks from the students of Delhi
Step 1. Find the students of Mumbai
Step 2. Find their max marks using the sublist in step 1

MySQL Views
A view is a virtual table based on the result-set of an SQL statement.
*A view always shows up-to-date data. The
database engine recreates the view, every time a
user queries it.

DBMS and SQL(structured query language) .pptx

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