🎓 Lecture 1 — Types of SQL Statements (DDL vs. DML)

🧩 Overview

SQL statements are commands used to interact with tables (entities), columns (attributes), and rows (tuples) in a relational database.

They are grouped into two main categories — DDL and DML — each serving a different purpose.

⚙️ 1. Data Definition Language (DDL)

Used to define, modify, or remove database structures such as tables.

Common DDL commands:

Command Purpose
CREATE Creates new tables and defines columns.
ALTER Modifies an existing table — adds, drops, or changes column definitions.
TRUNCATE Deletes all rows in a table but keeps the table structure.
DROP Deletes the table entirely from the database.

➡️ Key idea: DDL deals with structure — how the database is built and organized.

🧮 2. Data Manipulation Language (DML)

Used to work with data stored in the tables — also known as CRUD operations:

Create, Read, Update, Delete.

Common DML commands:

Command Purpose
INSERT Adds new data rows into a table.
SELECT Retrieves (reads) data from a table.
UPDATE Modifies existing data in a table.
DELETE Removes data rows from a table.

➡️ Key idea: DML deals with data — how information inside tables is created and managed.

🧠 Quick Summary