Constraints help us to prevent invalid data entry into tables. Using constraints we can:

• • Enforce rules on the data in a table when ever a row is inserted, updated or deleted.
• • Prevents the deletion of a table if there are dependencies arising from other tables.

There are several constraints are as follows:

All constraints are stored in data dictionary. Constraints are easy to refer if we give them meaningful names. If we dont give a name to a constraint , the server gives a name by its own.