I get it now... project_id=115 has a frequency of 0.09241 in pg_stats.
So if ((project_id = 115) AND (project_id = 115)) is considered as two
independent conditions, the row estimate ends up being 0.09241 *
0.09241 * 1.20163e+07 (reltuples from pg_class) = 102614.
Quick follow up... I've found that the row estimate in:
explain select count(id) from versions where project_id IN (80,115)
AND project_id=115;
QUERY PLAN
Howdy, the query generator in my app sometimes creates redundant
filters of the form:
project_id IN ( list of projects user has permission to see ) AND
project_id = single project user is looking at
... and this is leading to a bad estimate (and thus a bad plan) on a
few complex queries. I've
