fix: do not remove DISTINCT based on a nullable UNIQUE constraint#1
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simonvandel merged 1 commit intoJul 16, 2026
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`ReplaceDistinctWithAggregate` removes `Distinct::All` when a
`Dependency::Single` functional dependence covers all input fields.
However a nullable UNIQUE constraint also produces a `Single`-mode
dependence, and SQL UNIQUE permits multiple NULL keys. DISTINCT treats
NULLs as equal, so it must still collapse those rows:
CREATE TABLE t (x INT UNIQUE) AS VALUES (NULL), (NULL), (1);
SELECT DISTINCT x FROM t;
returned two NULL rows.
Only remove the DISTINCT when the dependence is non-nullable or none of
its source fields are actually nullable, mirroring the guards already
used by `EliminateJoin` and `Filter::is_scalar`.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Proposed update to
Fixes this bug:
Before this PR: returned two NULL rows (three in total)
After this PR: returns 1 null row (two in total)
This was written by claude code and reviewed by me