If you can't fix your schema, there are a couple of options: 1. You can do you data access through sproc(s). That way you can check for this condition and not allow the insert. 2. You can implement a trigger to implement this constraint.
IT WOUld be helpful if u give me a simple example .... i would really appreciate it .. just simple sql stmts as to how to do it .. i have 8 cases all hardcoded so please .. thanku