Re: [HACKERS] Hypothetical suggestions for planner, indexing improvement

On Mon, May 05, 2003 at 09:33:33PM -0700, Josh Berkus wrote:
> EXISTS is more flexible than IN; how can you do a 3-column corellation on an
> IN clause?

It would be nice to add support for multi-column IN..

WHERE (a, b, c) IN (SELECT a, b, c ...)

BTW, does postgresql handle IN and EXISTS differently? Theoretically if
the optimizer was good enough you could transform one to the other and
not worry about it. Whenever possible, I try and use IN when the
subselect will return a very small number of rows, since IN might be
faster than EXISTS in that case, though it seems most optimizers tend to
fall apart when they see ORs, and a lot of databases transform IN to a
OR b OR c.
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