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https://issues.apache.org/jira/browse/CALCITE-3893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17079072#comment-17079072
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Vladimir Sitnikov commented on CALCITE-3893:
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[~julianhyde], as far as I understand, the current implementation makes the
plans a bit hard to implement.
In other words, it looks technically correct (e.g. we consider
{{LogicalAggregate(group=[{0}], groups=[[{0}, {}]], C=[COUNT()])}} to be OK
even though the second groups does not include `0` column), however, group=0,
groups={} does not have explicit way to express in SQL.
A naive approach would generate
{noformat}select dept, count(*) from emp group by grouping sets (()){noformat}
Of course `dept` is not grouped, so it would fail.
The implementation might indeed verify if {{dept}} is ever grouped and replace
all the occurrences with {{null}}, however, I guess it would help if Calcite
produced {{simplified}} plans (==the ones where known to be null columns are
already replaced with nulls).
WDYT?
> SQL with GROUP_ID may generate wrong plan
> -----------------------------------------
>
> Key: CALCITE-3893
> URL: https://issues.apache.org/jira/browse/CALCITE-3893
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.22.0
> Reporter: Shuo Cheng
> Assignee: Feng Zhu
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.23.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Consider the following SQL:
> {code:java}
> select
> deptno, group_id() as g, count(*) as c
> from emp
> group by grouping sets (deptno, (), ())
> {code}
> the plan after SqlToRel is:
> {code:java}
> LogicalUnion(all=[true])
> LogicalProject(DEPTNO=[$0], G=[0:BIGINT], C=[$1])
> LogicalAggregate(group=[{0}], groups=[[{0}, {}]], C=[COUNT()])
> LogicalProject(DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> LogicalProject(DEPTNO=[$0], G=[1:BIGINT], C=[$1])
> LogicalAggregate(group=[{0}], groups=[[{}]], C=[COUNT()])
> LogicalProject(DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
> I'm afraid there's some semantic problems here. As `groups` of the second
> Aggregate is empty, then what is `$0` meaning in the Project above it. Maybe
> that we want is:
> {code:java}
> LogicalUnion(all=[true])
> LogicalProject(DEPTNO=[$0], G=[0:BIGINT], C=[$1])
> LogicalAggregate(group=[{0}], groups=[[{0}, {}]], C=[COUNT()])
> LogicalProject(DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> LogicalProject(DEPTNO=[$0], G=[1:BIGINT], C=[$1])
> LogicalAggregate(group=[{0}], groups=[[{0}]], C=[COUNT()])
> LogicalProject(DEPTNO=[null])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]]){code}
> I noticed this is introduced by CALCITE-1824, cc [~donnyzone],
> [~vladimirsitnikov].
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