opt: add support for NULLS LAST with DISTINCT ON #93567
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This commit adds an exception for the requirement that the ORDER BY clause of a DISTINCT ON query must contain only columns in the ON clause. Specifically, it allows expressions of the form `col IS NULL`, where col is one of the ON columns. This is needed to support NULLS LAST, since we implement NULLS LAST by synthesizing a `col IS NULL` ordering column. The approach feels a bit hacky, but it seems like the smallest, lowest risk option available. Fixes cockroachdb#90763 Release note (bug fix): Fixed an issue where DISTINCT ON queries would fail with the error "SELECT DISTINCT ON expressions must match initial ORDER BY expressions" when the query included an ORDER BY clause containing ASC NULLS LAST or DESC NULLS FIRST.
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msirek
approved these changes
Dec 14, 2022
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Nice fix!
Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @michae2)
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This was referenced Dec 14, 2022
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This commit adds an exception for the requirement that the
ORDER BYclause of aDISTINCT ONquery must contain only columns in theONclause. Specifically, it allows expressions of the formcol IS NULL, wherecolis one of theONcolumns. This is needed to supportNULLS LAST, since we implementNULLS LASTby synthesizing acol IS NULLordering column.The approach feels a bit hacky, but it seems like the smallest, lowest risk option available.
Fixes #90763
Release note (bug fix): Fixed an issue where
DISTINCT ONqueries would fail with the error "SELECT DISTINCT ON expressions must match initial ORDER BY expressions" when the query included anORDER BYclause containingASC NULLS LASTorDESC NULLS FIRST.