Data Definition Language (DDL)

CREATE TABLE

CREATE TABLE table_name (
  column1 datatype constraints,
  column2 datatype constraints,
  ...
);

Example

CREATE TABLE employees (
  employee_id INT PRIMARY KEY,
  first_name VARCHAR(50) NOT NULL,
  last_name VARCHAR(50) NOT NULL,
  email VARCHAR(100) UNIQUE,
  hire_date DATE,
  salary DECIMAL(10,2)
);

ALTER TABLE

Add Column

ALTER TABLE table_name ADD column_name datatype;

Modify Column

ALTER TABLE table_name MODIFY column_name new_datatype;

Drop Column

ALTER TABLE table_name DROP COLUMN column_name;

DROP TABLE

DROP TABLE table_name;

TRUNCATE TABLE

TRUNCATE TABLE table_name;

Constraints

• PRIMARY KEY: Unique identifier
• FOREIGN KEY: References another table
• UNIQUE: No duplicate values
• NOT NULL: Required value
• CHECK: Custom validation rule
• DEFAULT: Default value when none provided