francis0407 commented on issue #24344: [SPARK-27440][SQL] Optimize uncorrelated predicate subquery URL: https://github.com/apache/spark/pull/24344#issuecomment-486334094 Hard to find a SQL spec :( But the document I referenced above(https://dev.mysql.com/doc/refman/8.0/en/subquery-optimization-with-exists.html) explains how it behaves: > According to the SQL interpretation of NULL as “unknown value,” NULL IN (SELECT inner_expr ...) should evaluate to: > NULL, if the SELECT produces any rows > FALSE, if the SELECT produces no rows As for the normal IN, I think it should be consistent with InSubquery. I have tested in Postgres(only `select null in (1);`, not sure how to express `select null in array()` in it), and it returns the same as InSubquery.
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