> > I will check DB2 tomorrow.
>
> Here is what actually written SQL99:
>
> " A table check constraint is described by a table check constraint
> descriptor. In addition to the components of every table constraint
> descriptor, a table check constraint descriptor includes:
> - The <search condition>.
>
> A table check constraint is satisfied if and only if the specified
> <search condition> is not false for any row of a table."
>
> Though standard does not say that we cannot put subqueries into the
> search condition.
>
> And finally I have checked DB2. They simply do not allow subqueries in
> CHECK constraints.

Funny. This seems to be the case for all engines
NOT IN ('Firebird', 'InterBase').

This makes CHECK CONSTRAINTs very powerfull,
that is, IF they were to be checked correctly.

With regards,

Martijn Tonies
Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL
Server.
Upscene Productions
http://www.upscene.com