Types of SQL Commands

Types of SQL Commands-tutorial

SQL (Structured Query Language) is used to manage and interact with databases.

But all SQL commands are not the same they serve different purposes.

So, SQL commands are categorized into five main types, each handling a specific part of database operations.

What Are SQL Commands?

SQL commands are instructions you give to a database.

They tell the database what to do like creating a table, inserting data, or giving permission to users.

1. DDL – Data Definition Language

Purpose: Defines or changes the structure of the database (like tables, columns, etc.)

Command	Description	Example
CREATE	Creates a new database object (table, view, etc.)	CREATE TABLE Students (ID INT, Name VARCHAR (50));
ALTER	Modifies an existing table structure	ALTER TABLE Stdents ADD Age INT;
DROP	Deletes an existing database object	DROP TABLE Students;
TRUNCATE	Removes all data from a table but keeps structure	TRUNCATE TABLE Students;

DDL commands auto-save changes, so they cannot be rolled back easily.

2. DML – Data Manipulation Language

Purpose: Used to manipulate or manage data inside tables.

Command	Description	Example
INSERT	Adds new records	INSERT INTO Students VALUES (1, 'Amit', 22);
UPDATE	Modifies existing records	UPDATE Students SET Age = 23 WHERE ID = 1;
DELETE	Removes records	DELETE FROM Students WHERE ID = 1;
SELECT	Retrieves data from tables	SELECT * FROM Students;

DML commands can be rolled back if changes are not committed.

3. DCL – Data Control Language

Purpose: Controls access and permissions to the database.

Command	Description	Example
GRANT	Gives permission to users	GRANT SELECT ON Students TO user1;
REVOKE	Takes back permission	REVOKE SELECT ON Students FROM user1;

Used mostly by database administrators for security control.

4. TCL – Transaction Control Language

Purpose: Manages changes made by DML commands and controls transactions.

Command	Description	Example
COMMIT	Saves all change permanently	COMMIT;
ROLLBACK	Undo uncommitted changes	ROLLBACK;
SAVEPOINT	Creates a poin to rollback partially	SAVEPOINT save1;

TCL ensures data consistency and prevents data loss during transactions.

5. DQL – Data Query Language

Purpose: Retrieves data from the database.

It mainly includes the SELECT command.

SELECT Name, Age FROM Students WHERE Age > 20;

Note: Some databases consider SELECT under DML, but it is often treated as a separate DQL category.

Two Minute Drill