What are MySQL constraints?

As we know that constraint is a kind of limitation or restriction. Similarly, MySQL constraints are used to define some rules that limit the data that can go into a table. With the help of constraints, we can basically maintain the accuracy and integrity of the data inside the table.

Types of MySQL constraints

MySQL constraints are of two types −

• Column Level constraints − The constraints which are applied only to a particular column of the table and limits only column data are called column level constraints.
• Table Level constraints − The constraints which are applied to the whole table and limits whole table data are called table-level constraints.

Followings are some most common MySQL constraints −

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