SQL: Syntax

1. SQL Syntax Rules

  • SQL keywords are not case-sensitive (SELECT = select), but uppercase is preferred for readability.

  • Statements usually end with a semicolon ; (especially when running multiple statements).

  • Whitespace and line breaks don’t affect execution — they’re just for formatting.


2. Basic SQL Statement Structure

SELECT column1, column2, ...
FROM table_name
WHERE condition
GROUP BY column
HAVING condition
ORDER BY column ASC|DESC;


3. Common SQL Commands


a) Data Query Language (DQL)

Retrieve data from a table

SELECT first_name, last_name
FROM employees
WHERE department = 'HR'
ORDER BY last_name ASC;


b) Data Definition Language (DDL)

Create / modify / delete database objects

CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    salary DECIMAL(10,2)
);

ALTER TABLE employees ADD COLUMN department VARCHAR(50);

DROP TABLE employees;


c) Data Manipulation Language (DML)

Insert, update, delete data

INSERT INTO employees (id, name, salary) 
VALUES (1, 'John Doe', 50000);

UPDATE employees
SET salary = 55000
WHERE id = 1;

DELETE FROM employees
WHERE id = 1;


d) Data Control Language (DCL)

Permissions and access control

GRANT SELECT, INSERT ON employees TO user1;
REVOKE INSERT ON employees FROM user1;


4. SQL Syntax Cheat Table

Command Purpose Example
SELECT Retrieve data SELECT * FROM users;
INSERT Add data INSERT INTO users VALUES (1,'Alice');
UPDATE Modify data UPDATE users SET age=30 WHERE id=1;
DELETE Remove data DELETE FROM users WHERE id=1;
CREATE Create objects CREATE TABLE orders (...);
DROP Delete objects DROP TABLE orders;
ALTER Modify objects ALTER TABLE orders ADD COLUMN date DATE;