opt: fix error caused by recursive CTE with zero rows on left side #49961
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Prior to this commit, a recursive CTE in which the cardinality of the left side of the UNION ALL expression was zero would cause an error in the statistics code, "estimated row count must be non-zero". This was happening because the cardinality of the recursive CTE binding props was set to be non-zero, but the row count, which came from the left side expression, was not updated accordingly. The stats code only allows the row count to be zero if the cardinality is also zero. This commit fixes the problem by setting the row count of the binding props to 1 if the estimated row count of the left side is less than 1. Fixes cockroachdb#49911 Release note (bug fix): Fixed an internal planning error that occured for recursive CTEs (WITH RECURSIVE expressions) in which the left side of the UNION ALL query used in the CTE definition produced zero rows.
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mgartner
approved these changes
Jun 8, 2020
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Reviewed 2 of 2 files at r1.
Reviewable status:complete! 1 of 0 LGTMs obtained (waiting on @RaduBerinde)
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TFTR! bors r+ |
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Prior to this commit, a recursive CTE in which the cardinality of
the left side of the
UNION ALLexpression was zero would cause anerror in the statistics code, "estimated row count must be non-zero".
This was happening because the cardinality of the recursive CTE binding
props was set to be non-zero, but the row count, which came from the
left side expression, was not updated accordingly. The stats code only
allows the row count to be zero if the cardinality is also zero.
This commit fixes the problem by setting the row count of the binding
props to 1 if the estimated row count of the left side is less than 1.
Fixes #49911
Release note (bug fix): Fixed an internal planning error that occured
for recursive CTEs (WITH RECURSIVE expressions) in which the left side
of the UNION ALL query used in the CTE definition produced zero rows.