>>My question was about preventing invalid input directly in tables. In forms I use Table buffering and catch all problems gracefully (or, at least, I hope so). However, if user just opens table in command window (use myTable), then append blank, my original procedure didn't prevent from 3 "0" despite the fact, that I have a PK set. I hope, that Steve's solution would work for these situations. I already implemented it, but haven't tested yet.
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>Nadya,
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>I don't see any difference here. Default values for a field apply when table is opened in a form, when the user opens the table in the command window, or even when the table is opened indirectly through a view.
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>Of course, the user can change the value later - but triggers, too, apply both in forms and in the command window.
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>Hilmar.

Hilmar,

All I'm saying is: I have a default value to be my SP function. In case something goes wrong, this function returned 0. User did three times Append blank, and all three times 0 was appended, which should not happen. Could it be a corrupted index or you think, Primary index would not prevent these things from happenning?