SQL Statements

SQL statements are the individual commands you use to interact with the database. Each statement tells the database what action to perform — from retrieving data to modifying the structure.

✍️ What Are SQL Statements?

A SQL statement is a complete instruction made up of one or more clauses. These statements can be grouped into several categories based on their purpose:

Data Query Language (DQL) – Retrieve data (SELECT)
Data Manipulation Language (DML) – Modify data (INSERT, UPDATE, DELETE)
Data Definition Language (DDL) – Define or alter database objects (CREATE, ALTER, DROP)
Data Control Language (DCL) – Manage permissions (GRANT, REVOKE)
Transaction Control Language (TCL) – Manage transactions (COMMIT, ROLLBACK, SAVEPOINT)

⚙️ Common SQL Statements Overview

Category	Statement	Purpose	Example
DQL	`SELECT`	Retrieve data from tables	`SELECT * FROM employees;`
DML	`INSERT`	Add new records	`INSERT INTO employees (name) VALUES ('Alice');`
	`UPDATE`	Modify existing records	`UPDATE employees SET age = 30 WHERE id = 1;`
	`DELETE`	Remove records	`DELETE FROM employees WHERE age < 20;`
DDL	`CREATE TABLE`	Create a new table	`CREATE TABLE employees (id INT, name VARCHAR(50));`
	`ALTER TABLE`	Change table structure	`ALTER TABLE employees ADD COLUMN salary INT;`
	`DROP TABLE`	Delete a table	`DROP TABLE employees;`
DCL	`GRANT`	Give permissions to users	`GRANT SELECT ON employees TO user1;`
	`REVOKE`	Remove permissions	`REVOKE SELECT ON employees FROM user1;`
TCL	`COMMIT`	Save all changes in a transaction	`COMMIT;`
	`ROLLBACK`	Undo changes since last COMMIT	`ROLLBACK;`

🧩 Statement Syntax Basics

Every SQL statement has:

A command keyword (e.g., SELECT, INSERT)
Optional clauses (e.g., WHERE, ORDER BY)
Terminates with a semicolon (;)

Example:

SELECT name, age
FROM employees
WHERE age > 25
ORDER BY age DESC;

💡 Tips to Remember

Always end statements with a semicolon.
Use uppercase for commands to improve readability.
Write one statement per query execution (unless your database supports batch execution).
Use comments (we’ll cover next) to explain complex queries.

🧠 Quick Recap

Key Point	Details
SQL Statement	Command instructing database action
Categories	DQL, DML, DDL, DCL, TCL
End with semicolon	Marks completion of statement
Write clear and readable	Use uppercase commands and formatting