Answer:   SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted.

Answer:   This constraints nothing but it will rule to enforce the rule on the table, like null constrinats , referential constriants , primarykey constriaints . If any of these rull will violate the rule , it will throws as error message.