First cut at implementing IN (and NOT IN) via hashtables. There is

Tom Lane <tgl@sss.pgh.pa.us>

Commit: 19b886332a76f6b1141a7c1ca1d9eacaa8ef40d2
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2003-01-12T04:03:34Z
Releases: 7.4.1
First cut at implementing IN (and NOT IN) via hashtables.  There is
more to be done yet, but this is a good start.

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