On Thu, 5 Jan 2023 at 16:12, Tom Lane <t...@sss.pgh.pa.us> wrote: > > David Rowley <dgrowle...@gmail.com> writes: > > Additionally, it's also not that clear to me that sorting by more > > columns in the sort below the WindowAgg would always be a win over > > doing the final sort for the ORDER BY. What if the WHERE clause (that > > could not be pushed down before a join) filtered out the vast majority > > of the rows before the ORDER BY. It might be cheaper to do the sort > > then than to sort by the additional columns earlier. > > That's certainly a legitimate question to ask, but I don't quite see > where you figure we'd be sorting more rows? WHERE filtering happens > before window functions, which never eliminate any rows. So it seems > like a sort just before the window functions must sort the same number > of rows as one just after them.
Yeah, I didn't think the WHERE clause thing out carefully enough. I think it's only the WindowClause's runCondition that could possibly filter any rows between the Sort below the WindowAgg and before the ORDER BY is evaluated. David
