| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Decibel! <decibel(at)decibel(dot)org> |
| Cc: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: IN vs EXISTS equivalence |
| Date: | 2008-08-12 01:45:45 |
| Message-ID: | 24375.1218505545@sss.pgh.pa.us |
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| Thread: | |
| Lists: | pgsql-hackers |
Decibel! <decibel(at)decibel(dot)org> writes:
> On Aug 8, 2008, at 3:23 PM, Tom Lane wrote:
>> * has no set operations (UNION etc), grouping, set-returning functions
>> in the SELECT list, LIMIT, or a few other funny cases
> Couldn't union/union all be treated as
> EXISTS(a)
> OR EXISTS(b)
Perhaps, but that would end up defeating the optimization anyway,
because as soon as the EXISTS is underneath an OR, it's no longer
representing a potential join clause.
regards, tom lane
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