Thanks for your information, yes, with multiple columns equal join and correlation , looks like extended statistics could help reduce “significantly rows estimation”. Hopefully it’s in future version.
James From: Pavel Stehule <pavel.steh...@gmail.com> Sent: Tuesday, June 13, 2023 7:29 PM To: David Rowley <dgrowle...@gmail.com> Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>; James Pang (chaolpan) <chaol...@cisco.com> Subject: Re: extended statistics n-distinct on multiple columns not used when join two tables út 13. 6. 2023 v 13:26 odesílatel David Rowley <dgrowle...@gmail.com<mailto:dgrowle...@gmail.com>> napsal: (moving to -hackers) On Tue, 13 Jun 2023 at 21:30, Pavel Stehule <pavel.steh...@gmail.com<mailto:pavel.steh...@gmail.com>> wrote: > út 13. 6. 2023 v 11:21 odesílatel James Pang (chaolpan) > <chaol...@cisco.com<mailto:chaol...@cisco.com>> napsal: >> When join two table on multiple columns equaljoin, rows estimation >> always use selectivity = multiplied by distinct multiple individual columns, >> possible to use extended n-distinct statistics on multiple columns? >> >> PG v14.8-1, attached please check test case with details. > > There is not any support for multi tables statistic I think it's probably worth adjusting the docs to mention this. It seems like it might be something that could surprise someone. Something like the attached, maybe? +1 Pavel David
