Add constraint foreign key

To add constraint foreign key on a table of Oracle database you must use the alter table command and add constraint keyword.

Syntax

ALTER TABLE table_name1
ADD CONSTRAINT constraint_name
FOREIGN KEY (coll_name)
REFERENCES table_name2(coll_name);

Add constraint foreign key example

  
ALTER TABLE orders
ADD CONSTRAINT fk_course 
FOREIGN KEY (course_id)
REFERENCES course(course_id);

Output:

table ORDERS altered.

Check constraints

SELECT OWNER, CONSTRAINT_NAME, STATUS
FROM user_constraints
WHERE table_name = 'ORDERS';

Output:

OWNERCONSTRAINT_NAMESTATUS
SYSTEMFK_COURSEENABLED