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  • @FrustratedWithFormsDesigner: I know exactly what that means. select whatever from sometable where FKValue in (select FKValue from sometable_2 where other_value = :param). It should be trivial to see how to restate that with an exists or a join.
    – Mason Wheeler
    CommentedJun 3, 2013 at 20:47
  • Using similar reasoning I guess regular expressions are a more declarative method of expression as I rarely see performance questions answered by "you should write it this way to get better performance". I am wracking my brains and can half remember some question to do with negative look-behind or ahead assertions in a slow regexp where the answer was to rewrite the regexp in a different way to do the same in less time.
    – Paddy3118
    CommentedJun 3, 2013 at 21:16
  • Performance is an implementation detail. The performance of nearly any IN implementation could be comparable or better than EXISTS and JOIN if the query processor developers felt it was a priority.
    – JustinC
    CommentedJun 4, 2013 at 7:06
  • 1
    @JustinC, it seems to be more than a detail given the preponderance of performance oriented SQL questions and tips for a supposedly declarative language?
    – Paddy3118
    CommentedJun 4, 2013 at 12:34
  • There is no clear definition of a declarative programming language, and so it's meaningless to talk about. Some languages are higher-level than others, that's all.
    – gardenhead
    CommentedNov 6, 2016 at 17:15

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