Data Definition Language (DDL)
CREATE TABLE
Section titled “CREATE TABLE”CREATE TABLE table_name ( column1 datatype constraints, column2 datatype constraints, ...);Example
Section titled “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
Section titled “ALTER TABLE”Add Column
Section titled “Add Column”ALTER TABLE table_name ADD column_name datatype;Modify Column
Section titled “Modify Column”ALTER TABLE table_name MODIFY column_name new_datatype;Drop Column
Section titled “Drop Column”ALTER TABLE table_name DROP COLUMN column_name;DROP TABLE
Section titled “DROP TABLE”DROP TABLE table_name;TRUNCATE TABLE
Section titled “TRUNCATE TABLE”TRUNCATE TABLE table_name;Constraints
Section titled “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