>This is the question. Should I call the SQL table to check if user made a valid entry (by querying the primary table UNIQUE field) or rely on the constraint to catch the invalid entry. In the VFP back end I am using the index and SEEK for the value before writing update. I thought that to minimize the trips to SQL Server to simply make the data go only one time and rely on the constraint. The point is that SQL Server will check for the constraint anyway, why not rely on it for data validation?

If it FK constraint, I don't see why user should be allowed to enter anything that is not in the PK table for the FK.