8000 distinct aggregate should distinct on all arguments instead of only the first · Issue #10942 · risingwavelabs/risingwave · GitHub
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distinct aggregate should distinct on all arguments instead of only the first #10942

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stdrc opened this issue Jul 14, 2023 · 4 comments
Open

distinct aggregate should distinct on all arguments instead of only the first #10942

stdrc opened this issue Jul 14, 2023 · 4 comments
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A-agg Area: Aggregate. type/enhancement Type: Enhancement for an existing feature.

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@stdrc
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stdrc commented Jul 14, 2023 •
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Previously string_agg misbehave due to this issue if DistinctAggRule is not applied (#10826). After the fix #10864, string_agg now only allow constant delim when specifying DISTINCT option, while the issue still remains. Currently it doesn't cause any substantial harm, but may need to be fixed if users require multiple non-const distinct arguments when using later UDAF feature, so leave this issue just as a reminder.

cc @wangrunji0408
@stdrc stdrc added the type/feature Type: New feature. label Jul 14, 2023
@github-actions github-actions bot added this to the release-0.19 milestone Jul 14, 2023
@stdrc stdrc removed this from the release-0.19 milestone Jul 14, 2023
@fuyufjh fuyufjh added this to the release-1.1 milestone Jul 18, 2023
@xiangjinwu xiangjinwu modified the milestones: release-1.1, release-1.2 Aug 8, 2023
@st1page st1page modified the milestones: release-1.2, release-1.3 Sep 11, 2023
@stdrc stdrc modified the milestones: release-1.3, future-release-1.5 Oct 10, 2023
@fuyufjh fuyufjh modified the milestones: release-1.5, release-1.6 Dec 6, 2023
@wangrunji0408 wangrunji0408 modified the milestones: release-1.6, release-1.7 Jan 9, 2024
@wangrunji0408 wangrunji0408 modified the milestones: release-1.7, release-1.8 Mar 6, 2024
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github-actions bot commented Jul 3, 2024

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@stdrc stdrc removed this from the release-1.8 milestone Jul 23, 2024
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st1page commented Oct 29, 2024

IIUC, PG does not support that

postgres=# explain select count(distinct a,b) from t;
ERROR:  function count(integer, integer) does not exist
LINE 1: explain select count(distinct a,b) from t;
                       ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

But it support count(distinct (a,b)) or count(distinct ROW(a,b))

postgres=# explain select count(distinct (a,b)) from t;
                           QUERY PLAN
-----------------------------------------------------------------
 Aggregate  (cost=169.81..169.82 rows=1 width=8)
   ->  Sort  (cost=158.51..164.16 rows=2260 width=8)
         Sort Key: (ROW(a, b))
         ->  Seq Scan on t  (cost=0.00..32.60 rows=2260 width=8)
(4 rows)

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stdrc commented Nov 1, 2024 •
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IIUC, PG does not support that

postgres=# explain select count(distinct a,b) from t;
ERROR:  function count(integer, integer) does not exist
LINE 1: explain select count(distinct a,b) from t;
                       ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

I mean the functions that accept more than 1 arguments, e.g. string_agg. Example in PG:

create table t (a int, b int);
insert into t values (1, 1), (2, 2), (2, 3), (2, 2), (3, 3), (4, 4);

select string_agg(distinct a::text || ']', '[' || b::text) from t;

PG allows distinct in function call accepting multiple arguments, and the semantics is to distinct on all of the arguments. Currently we don't support this. For string_agg, this is not a big problem actually, however I think this may be useful when using UDAF.

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st1page commented Nov 4, 2024

PG allows distinct in function call accepting multiple arguments, and the semantics is to distinct on all of the arguments

appalled to know that

@stdrc stdrc self-assigned this Dec 10, 2024
@stdrc stdrc added A-agg Area: Aggregate. type/enhancement Type: Enhancement for an existing feature. and removed type/feature Type: New feature. labels May 26, 2025
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