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1e79f14798
If a scalar subquery is used with a binary predicate, or, used in an arithmetic expression, it must return only one row/column to be valid. If this cannot be guaranteed at parse time through a single row aggregate or limit clause, Impala fails the query like such. E.g., currently the following query is not allowed: SELECT bigint_col FROM alltypesagg WHERE id = (SELECT id FROM alltypesagg WHERE id = 1) However, it would be allowed if the query contained a LIMIT 1 clause, or instead of id it was max(id). This commit makes the example valid by introducing a runtime check to test if the subquery returns a single row. If the subquery returns more than one row, it aborts the query with an error. I added a new node type, called CardinalityCheckNode. It is created during planning on top of the subquery when needed, then during execution it checks if its child only returns a single row. I extended the frontend tests and e2e tests as well. Change-Id: I0f52b93a60eeacedd242a2f17fa6b99c4fc38e06 Reviewed-on: http://gerrit.cloudera.org:8080/9005 Reviewed-by: Alex Behm <alex.behm@cloudera.com> Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>