Class 11 Informatics Practices – Introduction to SQL Notes

NCERT Class 11 Informatics Practices Chapter 8 – Introduction to SQL.

1. What is a Database?

A database is an organized collection of related data stored in a structured way so that it can be easily accessed and managed.

Example

2. DBMS (Database Management System)

A DBMS is software that allows users to create, manage and manipulate databases.

Functions of DBMS

• Data storage
• Data retrieval
• Data modification
• Data security
• Data sharing

Examples of DBMS

• MySQL
• Oracle
• Microsoft SQL Server
• PostgreSQL

3. RDBMS (Relational Database Management System)

An RDBMS stores data in the form of tables consisting of rows and columns.

• Row → Record
• Column → Field

Example Table

4. What is SQL?

SQL (Structured Query Language) is used to communicate with a database.

Using SQL we can:

• Create databases
• Create tables
• Insert records
• Retrieve records
• Update records
• Delete records

Example Query

SELECT * FROM student;

This query displays all records from the student table.

5. Characteristics of SQL

• SQL is case insensitive
  ( SELECT
  select
  Select )
  All mean the same.
• SQL Commands end with a semicolon
  SELECT * FROM student;
• SQL Queries can be written in multiple lines

6. SQL Command Categories

1. DDL (Data Definition Language)

DDL commands define database structure.

Example

CREATE DATABASE SchoolDB;

7. CREATE TABLE

CREATE TABLE student(
rollno INT,
name CHAR(20),
class CHAR(5),
marks INT
);

8. INSERT Command

Used to insert records into a table.

INSERT INTO student
VALUES(101,'Rahul','XI',85);

9. SELECT Command

Used to retrieve data from tables.

SELECT * FROM student;

To display only specific columns:

SELECT name FROM student;

10. UPDATE Command

Used to modify existing records.

UPDATE student
SET marks = 88
WHERE rollno = 101;

11. DELETE Command

Used to remove records from a table.

DELETE FROM student
WHERE rollno = 103;

12. SQL Clauses

WHERE Clause

SELECT * FROM student
WHERE marks > 80;

ORDER BY Clause

SELECT * FROM student
ORDER BY marks DESC;

DISTINCT Clause

SELECT DISTINCT name
FROM student;

LIKE Clause

SELECT * FROM student
WHERE name LIKE 'R%';

13. Logical Operators

• AND
• OR
• NOT

Example

SELECT * FROM student
WHERE marks > 80 AND class = 'XI';

14. Important Database Terms

Important SQL Commands for Exams