opt: add rule to eliminate Exists when input has zero rows #48162
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This commit adds a new rule, EliminateExistsZeroRows, which converts an Exists subquery to False when it's known that the input produces zero rows. Informs cockroachdb#47058 Release note (performance improvement): The optimizer can now detect when an Exists subquery can be eliminated because the input has zero rows. This leads to better plans in some cases.
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complete! 1 of 0 LGTMs obtained (waiting on @mgartner and @RaduBerinde)
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Thanks for looking into the regression! I added an entry to #43438 to propagate soft-limit of 1 to Exists input (not exactly related to this change, but the tests around the rule that removes Limit made me think of it). |
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Reviewed 3 of 3 files at r1.
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TFTRs! And thanks for adding that TODO for soft-limit 1 for Exists, @RaduBerinde.
bors r+
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This commit adds a new rule,
EliminateExistsZeroRows, whichconverts an
Existssubquery to False when it's knownthat the input produces zero rows.
Informs #47058
Release note (performance improvement): The optimizer can now
detect when an Exists subquery can be eliminated because the input
has zero rows. This leads to better plans in some cases.