Julian Hyde created CALCITE-4719:
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             Summary: Add variants of RexSubQuery that collect sub-queries into 
MULTISET, ARRAY and MAP collections
                 Key: CALCITE-4719
                 URL: https://issues.apache.org/jira/browse/CALCITE-4719
             Project: Calcite
          Issue Type: Bug
         Environment: Add variants of {{RexSubQuery}} that collect sub-queries 
into {{MULTISET}}, {{ARRAY}} and {{MAP}} collections. We currently use 
{{RexSubQuery}} for scalar sub-query, {{EXISTS}}, {{IN}} and some others; this 
allows us to defer conversion: convert via rewrites ({{RelOptRule}}) rather 
than in {{SqlToRelConverter}}. The same benefits would apply to {{MULTISET}}, 
{{ARRAY}} and {{MAP}} sub-queries.

Examples:
{code}
SELECT deptno, MULTISET(SELECT * FROM Emp WHERE deptno = d.deptno)
FROM Dept AS d

SELECT deptno, ARRAY(SELECT * FROM Emp WHERE deptno = d.deptno)
FROM Dept AS d

SELECT deptno, MAP(SELECT empno, job FROM Emp WHERE deptno = d.deptno)
FROM Dept AS d
{code}

            Reporter: Julian Hyde






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