SQL statement categories (DDL, DML, DQL, DCL)

Introduction

SQL statements are grouped into categories to help us understand what each type does. This makes it easier to learn and use SQL for managing data and database structure.

When creating or changing the structure of a database, like adding tables or columns.

When adding, updating, or deleting data inside tables.

When retrieving data from the database to see or use it.

When controlling who can access or change the data.

Syntax

SQL

/* Categories of SQL statements */
-- DDL: Data Definition Language
CREATE TABLE table_name (...);
ALTER TABLE table_name ...;
DROP TABLE table_name;

-- DML: Data Manipulation Language
INSERT INTO table_name VALUES (...);
UPDATE table_name SET column = value WHERE ...;
DELETE FROM table_name WHERE ...;

-- DQL: Data Query Language
SELECT column1, column2 FROM table_name WHERE ...;

-- DCL: Data Control Language
GRANT privilege ON object TO user;
REVOKE privilege ON object FROM user;

Each category groups commands by their purpose.

Some commands may overlap but are mainly used in one category.

Examples

This is a DDL command to create a new table called Students.

SQL

CREATE TABLE Students (ID INT, Name VARCHAR(50));

This is a DML command to add a new row to the Students table.

SQL

INSERT INTO Students VALUES (1, 'Alice');

This is a DQL command to get the name of the student with ID 1.

SQL

SELECT Name FROM Students WHERE ID = 1;

This is a DCL command to give user1 permission to read data from Students.

SQL

GRANT SELECT ON Students TO user1;

Sample Program

This example shows creating a table, adding data, retrieving it, and giving access permission.

SQL

CREATE TABLE Employees (ID INT, Name VARCHAR(50));
INSERT INTO Employees VALUES (1, 'John');
INSERT INTO Employees VALUES (2, 'Jane');
SELECT * FROM Employees;
GRANT SELECT ON Employees TO user2;

Important Notes

DDL commands change the structure of the database.

DML commands change the data inside tables.

DQL commands read data without changing it.

DCL commands manage user permissions.

Summary

SQL statements are grouped into DDL, DML, DQL, and DCL categories.

Each category has a clear role: structure, data, query, or control.

Knowing these helps you use SQL effectively and understand what commands do.