Performance Comparation Between sql SELECT NULL and SELECT 1

Which one is better for performance

IF开发者_Python百科 EXISTS(Select null from table)

or

IF EXISTS(Select 1 from table)

?

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Both perform the same, because the SELECT clause in the EXISTS is never evaluated. You can test using:

... EXISTS(SELECT 1/0 FROM TABLE) 

That should trigger a divide by zero error, but won't.

I personally prefer using NULL because it's obvious that nothing is referenced in the table, so it's more visible to others. Selecting a value, like the INT number 1 in the second example, can lead to assumptions about what is happening if not familiar with the EXISTS clause.