Michael L John (12/17/2015)

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GilaMonster (12/17/2015)

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MMartin1 (12/17/2015)

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Does the SELECT 1 provide a big performance gain or just prevents a call to the disk that may get delayed?

Neither. It's there to show readers that EXISTS doesn't care about column names. You could do EXISTS (SELECT 1/0 ...) if you wanted.

Someone who shall remain nameless had a good blog post on this subject!

http://sqlinthewild.co.za/index.php/2011/04/05/to-top-or-not-to-top-an-exists/#more-988