InterBase Referential Integrity
This video covers (more reading from the InterBase DocWiki on the links here)
Tip for adding Constraints.
One very cool tip in the video is to use constraints to add in a unique key, this way you can drop it easily at runtime. Remember, the field needs to be marketed NOT NULL to enable a primary or unique key.
ALTER TABLE CUSTOMER ADD CONSTRAINT U_TEST UNIQUE (CUSTOMER_NAME);
The above example names the constraint U_TEST. (you can put whatever value you want in to name it, making it easy to drop with the following statement.
ALTER TABLE CUSTOMER DROP CONSTRAINT U_TEST;