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Introduction to Database

Presented By :- Avinash Agrawal

How to retrieve data from a database?

SQL QUERIES

Introduction to SQL.
• SQL stands for Structured Query Language
• SQL is a special-purpose programming
language designed for managing data in
database management systems (DBMS).
• SQL lets you access and manipulate databases
• SQL is an ANSI (American National Standards
Institute) standard.

What Can SQL do?
• SQL can execute queries against a database
• SQL can retrieve data from a database
• SQL can insert records in a database
• SQL can update records in a database
• SQL can delete records from a database
• SQL can create new databases
• SQL can create new tables in a database
• SQL can create stored procedures in a database
• SQL can create views in a database

SQL DML and DDL
• SQL can be divided into two parts: The Data
Manipulation Language (DML) and the Data
Definition Language (DDL).
DDL:- DML:-

CREATE DATABASE - creates a new
SELECT - extracts data from a
database
database
ALTER DATABASE - modifies a
UPDATE - updates data in a
database
database
CREATE TABLE - creates a new table
DELETE - deletes data from a
ALTER TABLE - modifies a table
database
DROP TABLE - deletes a table
INSERT INTO - inserts new
CREATE INDEX - creates an index
data into a database
(search key)
DROP INDEX - deletes an index

HOW TO CREATE A DATABASE AND A TABLE ?

• The CREATE DATABASE statement is used to create a database.
Syntax:-
• CREATE DATABASE database_name

CREATE DATABASE Example
We use the following CREATE DATABASE statement:
• CREATE DATABASE my_db

• The CREATE TABLE statement is used to create a table in a database.
Syntax:-
• CREATE TABLE table_name
(
column_name1 data_type,
....
)

Start with the table “persons”.

The SQL SELECT Statement

SQL SELECT Syntax:

SELECT
column_name(s)
FROM table_name

and
SELECT * FROM
table_name

The SQL SELECT DISTINCT Statement

In a table, some of the columns may contain duplicate values.
This is not a problem, however, sometimes you will want to list
only the different (distinct) values in a table.

The DISTINCT keyword can be used to return only distinct
(different) values.

SELECT DISTINCT SYNTAX:-
SELECT DISTINCT
column_name(s)
FROM table_name

SQL WHERE Clause:

The WHERE clause is used to extract only those records that fulfill
a specified criterion.

Syntax:
SELECT column_name(s)
FROM table_name
WHERE column_name operator value

Operators Allowed in the WHERE Clause

The ORDER BY Keyword:-
The ORDER BY keyword is used to sort the result-set by a specified
column.
The ORDER BY keyword sorts the records in ascending order by default.
If you want to sort the records in a descending order, you can use the
DESC keyword.

Syntax:-
FROM table_name
ORDER BY column_name(s) ASC|DESC

SQL INSERT INTO Statement

The INSERT INTO statement is used to insert a new row in a
table.

SYNTAX:-
INSERT INTO table_name
VALUES (value1, value2, value3,...)

SQL UPDATE Statement

The UPDATE statement is used to update existing records in
a table.
SQL UPDATE Syntax:-
UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value

SQL DELETE Statement

The DELETE statement is used to delete rows in a table.

SQL DELETE Syntax:-
DELETE FROM table_name
WHERE some_column=some_value

LIKE OPERATOR
The LIKE operator is used to search for a specified pattern in a column.
SQL LIKE Syntax
FROM table_name
WHERE column_name LIKE pattern

SQL Joins
The JOIN keyword is used in an SQL statement to query data
from two or more tables, based on a relationship between
certain columns in these tables.

Different SQL JOINs-

JOIN: Return rows when there is at least one match in both tables
LEFT JOIN: Return all rows from the left table, even if there are no matches in the right
table
RIGHT JOIN: Return all rows from the right table, even if there are no matches in the
left table
FULL JOIN: Return rows when there is a match in one of the tables

SQL INNER JOIN Keyword:-

The INNER JOIN keyword
return rows when there is at
least one match in both
tables.
SQL INNER JOIN Syntax
FROM table_name1
INNER JOIN table_name2
ON
table_name1.column_name=t
able_name2.column_name

SELECT Persons.LastName,
Persons.FirstName,
Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON
Persons.P_Id=Orders.P_Id
ORDER BY Persons.LastName

SQL LEFT JOIN Keyword:-

returns all rows from the left
table (table_name1), even if
there are no matches in the
right table (table_name2).
SQL LEFT JOIN Syntax
FROM table_name1
LEFT JOIN table_name2
ON

Persons.FirstName,
Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON

SQL RIGHT JOIN :-

The RIGHT JOIN keyword
returns all the rows from the
right table (table_name2),
even if there are no matches
in the left table
(table_name1).
SQL RIGHT JOIN Syntax
FROM table_name1
RIGHT JOIN table_name2
ON
Persons.FirstName,
Orders.OrderNo
FROM Persons
RIGHT JOIN Orders
ON

SQL FULL JOIN :-

The FULL JOIN keyword
return rows when there is a
match in one of the tables.
SQL FULL JOIN Syntax
FROM table_name1
FULL JOIN table_name2
ON
table_name1.column_nam
e=table_name2.column_na
me

Persons.FirstName,
Orders.OrderNo
FROM Persons
FULL JOIN Orders
ON

VIEW:-
A view is a virtual table based on the result-set of an SQL
statement.
A view contains rows and columns, just like a real table. The fields
in a view are fields from one or more real tables in the database.

SQL CREATE VIEW Syntax:-

CREATE VIEW view_name AS
FROM table_name
WHERE condition

SQL Creating a View SQL Updating a View SQL Dropping a View

In SQL, a view is a virtual table You can update a view by You can delete a view with the
based on the result-set of an using the following syntax: DROP VIEW command.
SQL statement.
SQL CREATE OR REPLACE VIEW SQL DROP VIEW Syntax:-
SQL CREATE VIEW Syntax:- Syntax:-
DROP VIEW view_name
CREATE VIEW view_name AS CREATE OR REPLACE VIEW
SELECT column_name(s) view_name AS
FROM table_name SELECT column_name(s)
WHERE condition FROM table_name
WHERE condition
For example,
CREATE VIEW [Current Product
CREATE VIEW [Current Product List] AS
List] AS SELECT
SELECT ProductID,ProductName,Categ
ProductID,ProductName ory
FROM Products FROM Products
WHERE Discontinued=No WHERE Discontinued=No

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