Enabling a Constraint

You can enable an existing constraint using the ENABLE CONSTRAINT clause of ALTER TABLE.

ALTER TABLE employee
ENABLE CONSTRAINT your_constraint_name;

To enable a constraint, all the rows in the table must satisfy the constraint. You can apply a constraint to new data only by specifying ENABLE NOVALIDATE:

ALTER TABLE employee
ENABLE NOVALIDATE CONSTRAINT your_constraint_name;

The default is ENABLE VALIDATE, which means existing rows must pass the constraint check.

1. Adding a Constraint with CHECK
2. Adding a NOT NULL Constraint
3. Adding a FOREIGN KEY Constraint
4. ON DELETE CASCADE
5. ON DELETE SET NULL
6. Adding a UNIQUE Constraint
7. CHECK constraint
8. Multiple Constraints
9. Dropping a Constraint
10. Disabling a Constraint
11. Enabling a Constraint
12. Deferred Constraints
13. Getting Information on Constraints:user_constraints and all_constraints