[jira] [Commented] (CALCITE-4906) Wrong result for scalar subquery (single value aggregation) from empty input

["Julian Hyde (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-4906?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17450077#comment-17450077 ] 

Julian Hyde commented on CALCITE-4906:
--------------------------------------

I agree; the query should return NULL. 

Calcite has two ways of expanding sub-queries - in SqlToRel and using RexSubQuery. Do they both yield the incorrect result?

> 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
>            Priority: Major
>
> 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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