MySQL database Constraints

MySQL database Constraints

Database constraints:
A constraint is a data validation rule enforced on a table. It is mainly used to ensure data integrity in the database.
In addition, when the data in the table is mutually dependent, the related data is not deleted.


Constraints on data columns can be divided into the following two types:
Single Column constraint: each constraint only limits one column.
Multi-column constraints: each constraint can constrain multiple data Columns


There are two opportunities to specify constraints for a data table:
Specify constraints for corresponding data columns when creating a table
After creating a table, add constraints by modifying the table.

Most databases support the following five integrity constraints: