SQL Q. Using USER function in constraints

Hi all, I'm trying to add a constraint to an already existing database such that when a row is inserted or updated one of the rows cannot be equal to the user doing the insert or update. I decided to use the alter table add constraint statement in the following way: alter table coffeemade add constraint check (maker not in (USER)) but this just returns a syntax error every time ( error 201 in Informix 5 ), and seemingly points out that the use of the USER function is incorrect. If I substitute USER with another row in the table, say logger, then the constraint is added okay. As I understand it from reading the SQL reference manual its okay to use USER in such away ( theres even an example of USER being used like this ). Has anyone any ideas of where I'm going wrong, or even any alternative ways of getting the same effect using some other method. Thanks Andrew Hird -- ------------------------------------------------------ Andrew Hird, (IS Eng) andyh@sage.compnews.co.uk "Wake up Harry. You're having a very important nightmare!" - Wild Palms