John Mitchell-245523 (4/26/2013)
Use DISTINCT when you want to eliminate duplicates from your result test. If you use it in an existence test, like you did in your original post, then it won't make any difference to the results. That applies whether the column has a unique/PK constraint or not.John
+1
DISTINCT used in the EXISTS check is logically irrelevant. Check the plans - it may even be optimized away.
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