1) SQL commands ko categories me kyun baantte hain?

Kyuki SQL me alag-alag kaam hote hain:

• schema banana/modify karna (structure)
• data read karna
• data insert/update/delete karna
• permissions manage karna
• transactions (commit/rollback) manage karna

Isliye 5 categories famous hain: DDL, DQL, DML, DCL, TCL

2) DDL — Data Definition Language (Schema/Structure)

DDL ka matlab: database ka structure define/modify karna.

Ye “table banani hai”, “column add karna”, “table delete karni hai” type ka kaam.

Commands:

CREATE

• CREATE DATABASE
• CREATE TABLE
• CREATE VIEW

Example:

CREATE TABLE customer (
  id INT PRIMARY KEY,
  name VARCHAR(100) NOT NULL
);ALTER

Table structure change: