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(parent: 495d327) | patch
Fix estimate_num_groups() to assume that GROUP BY expressions yielding boolean
authorTom Lane <tgl@sss.pgh.pa.us>
Mon, 7 Jul 2008 20:25:14 +0000 (20:25 +0000)
committerTom Lane <tgl@sss.pgh.pa.us>
Mon, 7 Jul 2008 20:25:14 +0000 (20:25 +0000)
commit1b3dfb041a63d0f8d4ef8618b04b80fcedb8b4d7
treef7e7b46f9fb250d51576bdc4888fc10329773cd9tree
parent495d327b114a42f547cc13266a25ee98ab84cc84commit | diff
Fix estimate_num_groups() to assume that GROUP BY expressions yielding boolean
results always contribute two groups, regardless of the expression contents.
This is very substantially more accurate than the regular heuristic for
certain boolean tests like "col IS NULL".  Per gripe from Sam Mason.

Back-patch to all supported releases, since the behavior of
estimate_num_groups() hasn't changed all that much since 7.4.
src/backend/utils/adt/selfuncs.c diff | blob | blame | history
Kevin Grittner's development, especially fully serializable transactions (See http://wiki.postgresql.org/wiki/Serializable for more info)