> Richard A. Wilson wrote:
> cant you just index both fields and use your check index logic

That's what I do now, but there's no guarantee of uniqueness.  The key
is guaranteed unique-- you just can't write two records with the same
key.  But AFAIK nothing is going to stop me writing two records with a
data field set to the same value.  

I think I have concurrency issues-- if two users try for the same UserID
at the same time, they could both "think" they've got it.  (Same code
running twice, one just after the other.)

That's why I'm thinking to use a database trigger to move that final
check as close to the write as possible.

-- 
Wendy Smoak
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