| From: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Daniel Gustafsson <daniel(at)yesql(dot)se>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Avoid extra Sort nodes between WindowAggs when sorting can be reused |
| Date: | 2018-09-13 00:28:49 |
| Message-ID: | 87efdynxay.fsf@news-spur.riddles.org.uk |
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| Lists: | pgsql-hackers |
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
Tom> * I'm almost thinking that changing to list_union is a bad idea,
A fair point. Though it looks like list_union is used in only about 3
distinct places, and two of those are list_union(NIL, blah) to simply
remove dups from a single list. The third place is the cartesian-product
expansion of grouping sets, which uses list_union_int to remove
duplicates - changing the order there will give slightly user-surprising
but not actually incorrect results.
Presumably list_concat_unique should be considered to guarantee that it
preserves the relative order of the two lists and of the non-duplicate
items in the second list?
--
Andrew (irc:RhodiumToad)
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