Re: Plan weirdness. A sort produces more rows than the node beneath it

Dane Foster <studdugie@gmail.com> writes:
>> If the sort is the inner input to a merge join, this could reflect
>> mark-and-restore rescanning of the sort's output.  Are there a
>> whole lot of duplicate keys on the merge's other side?

> Yes. The course_id column's values repeat a LOT on the merge side.

Hmm.  The planner should avoid using a merge join if it knows that
to be true.  Maybe analyze'ing that table would prompt it to use
some other join method?

            regards, tom lane