DBMS UNIT 5 : SQL (Part 1) – Data Definition Language (DDL)

Database Management System

SQL (Structured Query Language)

A standard programming language used to manage and manipulate relational databases.

Data Definition Language (DDL)

A subset of SQL used to define and modify the structure of database objects like tables and schemas.

CREATE TABLE

A SQL command that creates a new table in the database with specified columns and data types.

DROP TABLE

A SQL command used to delete an existing table and all its data permanently from the database.

ALTER TABLE

A SQL command used to modify an existing table structure (e.g., add or drop columns, rename table).

PRIMARY KEY

A constraint that uniquely identifies each record in a table; cannot be null or duplicated.

FOREIGN KEY

A constraint used to link two tables; it ensures referential integrity by pointing to the primary key of another table.

NOT NULL

A constraint that ensures a column cannot have NULL values.

UNIQUE

A constraint that ensures all values in a column are distinct from one another.

AUTO_INCREMENT

A property that automatically generates a unique number when a new record is inserted (often used for primary keys).

DECIMAL(p, d)

A numeric data type where p is the precision (total digits) and d is the scale (digits after decimal point).