DongShengHe created CALCITE-7679:
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Summary: RelToSqlConverter generates GROUP BY literals for
dialects that do not support them when the constant is hidden by nested Projects
Key: CALCITE-7679
URL: https://issues.apache.org/jira/browse/CALCITE-7679
Project: Calcite
Issue Type: Bug
Reporter: DongShengHe
h3. Description
{{RelToSqlConverter}} may generate a literal in the {{GROUP BY}} clause for
dialects that do not support them when the grouping expression is hidden behind
multiple {{Project}} nodes.
This is related to CALCITE-4702. Its fix uses
{{AggregateProjectConstantToDummyJoinRule}} for dialects that do not support
grouping by literals. However, the rule only examines the {{Project}} directly
below the {{{}Aggregate{}}}.
For example, consider the following relational plan:
{code:java}
LogicalAggregate(group=[{0}])
LogicalProject(ID=[$0])
LogicalProject(ID=[null:NULL])
LogicalTableScan(table=[[hr, emps]]) {code}
{{{}{}}}{{{}{}}}
The direct project expression is {{{}$0{}}}, so
{{AggregateProjectConstantToDummyJoinRule}} does not recognize it as a literal.
As a result, the PostgreSQL dialect generates:
{code:java}
SELECT NULL AS "ID"
FROM "hr"."emps"
GROUP BY NULL {code}
{{}}
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