I know the idea has come up a few times to do cross-column statistics to improve plans when the data distributions are dependent. I found a couple references in the archives: http://archives.postgresql.org/pgsql-hackers/2006-09/msg02118.php http://archives.postgresql.org/pgsql-hackers/2006-08/msg00924.php We can already keep stats for a functional index. Is there a reason we can't keep stats for a multi-column index? Out of the two situations outlined by Jim Nasby here: http://archives.postgresql.org/pgsql-hackers/2006-08/msg00948.php It would not help with joins, but it would help with columns that are referred to as a group (e.g. a=1 AND b<20). Regards,Jeff Davis
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