SQL Constraints

From http://www.w3schools.com (Copyright Refsnes Data)

# SQL Constraints

Constraints are used to limit the type of data that can go into a table.

Constraints can be specified when a table is created (with the CREATE TABLE statement) or after the table is created (with the ALTER TABLE statement).

We will focus on the following constraints:

- NOT NULL
- UNIQUE
- PRIMARY KEY
- FOREIGN KEY
- CHECK
- DEFAULT

The next chapters will describe each constraint in details.

From http://www.w3schools.com (Copyright Refsnes Data)