fix(optimizer): retain set-returning projections in pushdown_projections#7686
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A projection containing a set-returning (table) function such as EXPLODE/POSEXPLODE/INLINE/UNNEST multiplies the rows of the entire query, so it affects the cardinality of every output column. Pruning such a projection because it is otherwise unreferenced silently changes the result's row multiset, which is a correctness bug. Keep any unused projection whose expression contains a set-returning function. Window functions (e.g. ROW_NUMBER() OVER (...)) do not change cardinality and remain prunable; LATERAL VIEW is already retained.
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SQLGlot Integration Test ResultsComparing:
By Dialect
Overallmain: 113231 total, 112181 passed (pass rate: 99.1%) sqlglot:retain-set-returning-projections: 101037 total, 101037 passed (pass rate: 100.0%) Transitions: Dialect pair changes: 0 previous results not found, 3 current results not found ✅ 64 test(s) passed |
georgesittas
approved these changes
May 28, 2026
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Problem
pushdown_projectionsremoves any projection that the outer query doesn't reference. But a projection whose expression is a set-returning / table function (EXPLODE,POSEXPLODE,INLINE,UNNEST) multiplies the rows of the entire query, so dropping it because it's otherwise unused silently changes the result's row cardinality:Fix
Retain any otherwise-unused projection whose expression contains a set-returning function.
Posexplodeand the*Outervariants subclassExplode, so matchingExplodecovers them. Window functions are not set-returning and remain prunable;LATERAL VIEWis already retained.Tests
Added fixtures to
tests/fixtures/optimizer/pushdown_projections.sqlcovering EXPLODE / POSEXPLODE / INLINE retention and ROW_NUMBER pruning. The full optimizer suite passes.