On Sat, 13 Jun 2020 at 15:11, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > I expect you're getting a fairly decent estimate for the "contype <> > ALL" condition, but the planner has no idea what to make of the CASE > construct, so it just falls back to a hard-wired default estimate. This feels quite similar to [1]. I wondered if it would be more simple to add some smarts to look a bit deeper into case statements for selectivity estimation purposes. An OpExpr like: CASE c.contype WHEN 'c' THEN 'CHECK' WHEN 'f' THEN 'FOREIGN KEY' WHEN 'p' THEN 'PRIMARY KEY' WHEN 'u' THEN 'UNIQUE' END = 'CHECK'; could be simplified to c.contype = 'c', which we should have statistics for. There'd certainly be case statement forms that couldn't be simplified, but I think this one could. David [1] https://www.postgresql.org/message-id/flat/CAApHDvr%2B6%3D7SZBAtesEavgOQ0ZC03syaRQk19E%2B%2BpiWLopTRbg%40mail.gmail.com#3ec465f343f1204446941df29fc9e715
