>>Looks like a good idea.
>>
>>What if we work with buffered tables? We may still need a candidate index.
>
>Regarding buffered tables, I am not sure, but it has never been an issue for me. Since three fields are involved, you would need a surrugate key as a candidate index, I don't like surrugate keys.

I agree, but I don't see a reliable way otherwise in multi-user environment using buffered data.