Question : Circular referential integrity problems

I have 4 tables which are all interconnected

Table Z has a primary key PKZ
Table C has a primary key PKC

Table C has a foreign key to table Z
Table A has a foreign key to table C and a foreign key to table Z
Table T has 2 foreign keys to table C  and a foreign key to table Z

All foreign keys may be nulls in certain circumstances.

I want to enforce referential integrity on all updates but can't because of the circular relationships.

Can anyone advise how I can redesign, reindex, re-anything to get round the problem ?

Answer : Circular referential integrity problems

> foriegn keys can't have nulls <

Yes they can.

Mamine: don't cascade updates. If you have a proper primary key, why would you ever change it? You still want foreign keys (to make sure you don't get orphaned records), but cascading updates? Naaah.