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).

CREATE DATABASE - creates a new databaseALTER DATABASE - modifies a databaseCREATE TABLE - creates a new tableALTER TABLE - modifies a tableDROP TABLE - deletes a tableCREATE INDEX - creates an index (search key)DROP INDEX - deletes an index

SELECT - extracts data from a databaseUPDATE - updates data in a databaseDELETE - deletes data from a databaseINSERT INTO - inserts new data into a database

DDL:- DML:-

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,column_name2 data_type,column_name3 data_type,....)

Start with the table “persons”.

The SQL SELECT Statement

SQL SELECT Syntax:

SELECT column_name(s)FROM table_name

andSELECT * 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_nameWHERE column_name operator value

Operators Allowed in the WHERE Clause

SQL AND & OR Operators

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:-SELECT column_name(s)FROM table_nameORDER 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_nameVALUES (value1, value2, value3,...)

SQL UPDATE Statement

The UPDATE statement is used to update existing records in a table.SQL UPDATE Syntax:- UPDATE table_nameSET 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_nameWHERE some_column=some_value

The LIKE operator is used to search for a specified pattern in a column.SQL LIKE SyntaxSELECT column_name(s)FROM table_nameWHERE column_name LIKE pattern

LIKE OPERATOR

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 tablesLEFT JOIN: Return all rows from the left table, even if there are no matches in the right tableRIGHT JOIN: Return all rows from the right table, even if there are no matches in the left tableFULL 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 SyntaxSELECT column_name(s)FROM table_name1INNER JOIN table_name2ON table_name1.column_name=table_name2.column_name

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM PersonsINNER JOIN OrdersON Persons.P_Id=Orders.P_IdORDER 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 SyntaxSELECT column_name(s)FROM table_name1LEFT JOIN table_name2ON table_name1.column_name=table_name2.column_name

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM PersonsLEFT JOIN OrdersON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName

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 SyntaxSELECT column_name(s)FROM table_name1RIGHT JOIN table_name2ON table_name1.column_name=table_name2.column_name

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM PersonsRIGHT JOIN OrdersON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName

SQL FULL JOIN :-

The FULL JOIN keyword return rows when there is a match in one of the tables.SQL FULL JOIN SyntaxSELECT column_name(s)FROM table_name1FULL JOIN table_name2ON table_name1.column_name=table_name2.column_name

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNoFROM PersonsFULL JOIN OrdersON Persons.P_Id=Orders.P_IdORDER BY Persons.LastName

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 ASSELECT column_name(s)FROM table_nameWHERE condition

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

You can delete a view with the DROP VIEW command.

SQL DROP VIEW Syntax:-

DROP VIEW view_name

You can update a view by using the following syntax:

SQL CREATE OR REPLACE VIEW Syntax:-

CREATE OR REPLACE VIEW view_name ASSELECT column_name(s)FROM table_nameWHERE condition

CREATE VIEW [Current Product List] ASSELECT ProductID,ProductName,CategoryFROM ProductsWHERE Discontinued=No

In SQL, a view is a virtual table based on the result-set of an SQL statement.

SQL CREATE VIEW Syntax:-

CREATE VIEW view_name ASSELECT column_name(s)FROM table_nameWHERE condition

For example,

CREATE VIEW [Current Product List] ASSELECT ProductID,ProductNameFROM ProductsWHERE Discontinued=No