fix: eliminate group by constant empty input#22132
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HairstonE wants to merge 3 commits into
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kumarUjjawal
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We should also add this test SELECT AVG(v1) FROM t1 GROUP BY false;
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Also could you add a non-empty positive case alongside the empty-table reproducer?
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Yeah I'll add those now. Added those tests.
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Which issue does this PR close?
Closes #11748
Rationale for this change
EliminateGroupByConstantstrips constant expressions from GROUP BY. When it strips all of them, it converts a grouping aggregate into a global aggregate. A grouping aggregate returns 0 rows on empty input, a global aggregate returns 1.GROUP BY false HAVING falseshould return 0 rows. It was returning 1 row of NULL.Found the root cause by reading PR #11897.
What changes are included in this PR?
The guard now bails out whenever all GROUP BY expressions are constants, regardless of whether aggregate functions exist. One line change, plus updated tests.
Are these changes tested?
Yes. Sqllogictest reproducer for the original issue, updated unit test and optimizer SLT expectations.
Are there any user-facing changes?
Queries with all-constant GROUP BY may now return fewer (correct) rows.