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

Roll No	Name	Class	Marks
101	Rahul	XI	85
102	Priya	XI	92

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

RollNo	Name	Class
101	Rahul	XI
102	Riya	XI

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.

Command	Purpose
CREATE	Create database or table
ALTER	Modify table structure
DROP	Delete table or database
DESC	Display table 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

Term	Meaning
Table	Collection of rows and columns
Field	Column in a table
Record	Row containing complete information
Primary Key	Unique identifier of a record

Important SQL Commands for Exams