"David G. Johnston" <david.g.johnston@gmail.com> writes: > On Fri, Mar 7, 2025 at 5:05 PM Tom Lane <tgl@sss.pgh.pa.us> wrote: >> Perhaps the wording in section 7.2.5 could be improved; I agree >> that "evaluated in one pass" is capable of being read in more >> than one way, and it's not clear that it's referring to sorts. >> Do you have any suggestions for clearer wording?
> We seem to do quite a few things that we don't tell the user about. The > attached patch describes those things and adds an example demonstrating > their effects via an explain; which is the only way you can construct an > example for this material. > Considered a draft pending feedback to either throw it out in favor of a > one-word/one-line fix or support for going into this amount of detail.
Meh. This is detail that wasn't asked for and doesn't belong in this section anyway. (If we did want to write something like this, chapter 14 Performance Tips would be a more plausible home I think. That'd at least remove the problem of forward-referencing EXPLAIN output.)
Thank you for the input. I figured that would be the response and am fine with it. I took a look at Chapter 14 and agree it could fit there but that just brought up more thoughts. I'll start a separate thread for all that.
For a shorter fix
When multiple window functions are used, all the window functions having syntactically equivalent PARTITION BY and ORDER BY clauses in their window definitions are guaranteed to see the same ordering of the input rows, even if the ORDER BY does not uniquely determine the ordering.
WFM, the key point is removing the problematic wording and I do find this reads better in the end.
However, I'm having trouble understanding the purpose of the word "syntactically" here. Or even using the "clauses" at all. Why not:
"When multiple window functions are used, all the window functions having the same partitioning and ordering expressions in their window definitions are guaranteed to see the same ordering of the input rows, even if the ordering is not deterministic."
