roseduan opened a new pull request, #1941:
URL: https://github.com/apache/cloudberry/pull/1941
CXformSimplifyGbAgg::FDropGbAgg() drops a GROUP BY/DISTINCT's aggregate node
when the grouping columns cover a key derived from a UNIQUE or PRIMARY KEY
constraint, assuming the key already guarantees one row per value.
That's wrong for a plain UNIQUE column: SQL allows multiple NULLs in it
(NULL is never "equal" for uniqueness checks), but dedup must still collapse
those NULLs into one row.
Before:
create table repro (c0 numeric unique);
insert into repro values (1), (2), (null), (null), (null);
explain (costs off) select distinct c0 from repro;
Gather Motion 3:1 (slice1; segments: 3)
-> Seq Scan on repro -- no aggregate, all 5 rows returned
After:
Gather Motion 3:1 (slice1; segments: 3)
-> GroupAggregate
Group Key: repro.c0
-> Seq Scan on repro -- correctly returns 1, 2, NULL
Fix by also requiring every key column to be provably NOT NULL
(CExpression::DeriveNotNullColumns()) before dropping the aggregate. PRIMARY
KEY columns are always NOT NULL, so that case is unaffected.
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Fixes #ISSUE_Number
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