Aleksey Plekhanov created CALCITE-4906:
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Summary: Wrong result for scalar subquery (single value
aggregation) from empty input
Key: CALCITE-4906
URL: https://issues.apache.org/jira/browse/CALCITE-4906
Project: Calcite
Issue Type: Bug
Reporter: Aleksey Plekhanov
Scalar subqueries from the empty input return non-nullable type and in some
cases it leads to wrong results. For example:
{noformat}
SELECT (SELECT 1 FROM (SELECT NULL) WHERE 1 = 0)
{noformat}
Returns {{0}}, but expected {{NULL}} according to the SQL standard:
{noformat}
Let SS be a <scalar subquery>.
Case:
a) If the cardinality of SS is greater than 1 (one), then an exception
condition is raised: cardinality violation.
b) If the cardinality of SS is 0 (zero), then the value of the <scalar
subquery> is the null value.
c) Otherwise, let C be the column of <query expression> simply contained in SS.
The value of SS is the value of C in the unique row of the result of the
<scalar subquery>.
{noformat}
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