[8.x] ESQL: push down LIMIT past LOOKUP JOIN (#118495) #118648
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Fix elastic#117698 by enabling push down of `LIMIT` past `LEFT JOIN`s. There is a subtle point here: our `LOOKUP JOIN` currently _exactly preserves the number of rows from the left hand side_. This is different from SQL, where `LEFT JOIN` will return _at least one row for each row from the left_, but may return multiple rows in case of multiple matches. We, instead, throw multiple matches into multi-values, instead. (C.f. [tests that I'm about to add](https://github.com/elastic/elasticsearch/pull/118471/files#diff-334f3328c5f066a093ed8a5ea4a62cd6bcdb304b660b15763bb4f64d0e87ed7cR365-R369) that demonstrate this.) If we were to change our semantics to match SQL's, we'd have to adjust the pushdown, too.
alex-spies
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maxhniebergall
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Dec 16, 2024
Fix elastic#117698 by enabling push down of `LIMIT` past `LEFT JOIN`s. There is a subtle point here: our `LOOKUP JOIN` currently _exactly preserves the number of rows from the left hand side_. This is different from SQL, where `LEFT JOIN` will return _at least one row for each row from the left_, but may return multiple rows in case of multiple matches. We, instead, throw multiple matches into multi-values, instead. (C.f. [tests that I'm about to add](https://github.com/elastic/elasticsearch/pull/118471/files#diff-334f3328c5f066a093ed8a5ea4a62cd6bcdb304b660b15763bb4f64d0e87ed7cR365-R369) that demonstrate this.) If we were to change our semantics to match SQL's, we'd have to adjust the pushdown, too.
maxhniebergall
pushed a commit
to maxhniebergall/elasticsearch
that referenced
this pull request
Dec 16, 2024
Fix elastic#117698 by enabling push down of `LIMIT` past `LEFT JOIN`s. There is a subtle point here: our `LOOKUP JOIN` currently _exactly preserves the number of rows from the left hand side_. This is different from SQL, where `LEFT JOIN` will return _at least one row for each row from the left_, but may return multiple rows in case of multiple matches. We, instead, throw multiple matches into multi-values, instead. (C.f. [tests that I'm about to add](https://github.com/elastic/elasticsearch/pull/118471/files#diff-334f3328c5f066a093ed8a5ea4a62cd6bcdb304b660b15763bb4f64d0e87ed7cR365-R369) that demonstrate this.) If we were to change our semantics to match SQL's, we'd have to adjust the pushdown, too.
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Backports the following commits to 8.x: