What are constraints?

Constraints enforce rules on the tables.  Constraints prevent deletion of a table, if there are dependencies.  Oracle uses constraints to prevent invalid data entry into tables. [Updates and inserts].  The constraints applied must be satisfied for the successful operation.  The constraints are called integrity constraints  (i.e., to maintain security and integrity this means honesty and reliability) of the database.  An integrity constraint is a mechanism used by oracle to prevent invalid data entry into the table and inadvertent deletes.  So constraints enforce rules that the columns in a table have to confirm with.  The various types of Integrity constraints are:

• Domain Integrity Constraints

Not null Constraint

Check Constraint

• Entity Integrity Constraints

Unique Constraint

Primary Key

• Referential Integrity Constraints

Foreign Key