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Phil, I would suspect that the engine is _not_ smart enough to stop because it "knows" there would only be one hit. HOWEVER, I would also expect that the engine would opt to use the index that was enforcing the unique constraint and as such, would only read one row -- effectively the same thing. The answer to your question "Can one assume 100% that the optimizer/SQL engine will ..." is NO! The ONLY thing you CAN assume is that the engine will return the rows that meet your selection criteria in the order you specify. You can not assume how it will find those rows, nor can you assume the order in which they'll be returned unless you explicitly specify an order. -Walden ------------ Walden H Leverich III President & CEO Tech Software (516) 627-3800 x11 WaldenL@xxxxxxxxxxxxxxx http://www.TechSoftInc.com Quiquid latine dictum sit altum viditur. (Whatever is said in Latin seems profound.)
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