[jira] [Resolved] (CALCITE-3466) JDBC adapter incorrectly drops GROUP BY clause of sub-query

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

     [ https://issues.apache.org/jira/browse/CALCITE-3466?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Hyde resolved CALCITE-3466.
----------------------------------
    Resolution: Fixed

Fixed in [571cf95a|https://github.com/apache/calcite/commit/571cf95a1564c925bf73e4dae3a6c63199b17c4e]; thanks for the PR, [~wangweidong]!

Regarding the structure of the code. I took [~danny0405]'s suggested restructuring, then factored the logic into a private function {{needNewSubQuery}} that returns {{boolean}}. I hope people think it is an improvement.

> JDBC adapter incorrectly drops GROUP BY clause of sub-query
> -----------------------------------------------------------
>
>                 Key: CALCITE-3466
>                 URL: https://issues.apache.org/jira/browse/CALCITE-3466
>             Project: Calcite
>          Issue Type: Bug
>          Components: jdbc-adapter
>    Affects Versions: 1.21.0, 1.22.0
>            Reporter: Wang Weidong
>            Assignee: Wang Weidong
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.22.0
>
>         Attachments: screenshot-1.png
>
>          Time Spent: 8h 40m
>  Remaining Estimate: 0h
>
> While convert RelNode to SqlNode, the "group by" statement in subquery was dropped unexpectedly. For example,
> original sql is:
> {code:sql}
> select a, avg(c1) from 
> (
>     select a,sum(d),b as c1 from t group by b,a
> ) as t 
> group by a
> {code}
> RelNode converted by SqlNode is 
> {code:sql}
> LogicalAggregate(group=[{0}], EXPR$1=[AVG($1)])
>   LogicalProject(A=[$1], C1=[$0])
>     LogicalAggregate(group=[{0, 1}], EXPR$1=[SUM($2)])
>       LogicalProject(B=[$1], A=[$0], D=[$3])
>         EnumerableTableScan(table=[[T_TESTPROJECTMERGE]])
> {code}
> And then convert this RelNode to SqlNode, the sql of SqlNode is like this:
> {code:sql}
> SELECT `A`, AVG(`B`)
> FROM `T`
> GROUP BY `A`
> {code}
> We can find that "group by" in subquery was dropped which may cause SqlNode converted by RelNode being not equivalent to RelNode.
> After debugging, I've found code 
> at https://github.com/apache/calcite/blob/aa98c1575762718b238af8ddd44a390607de7602/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java#L333 
> calls org.apache.calcite.rel.rel2sql.SqlImplementor.Builder#setGroupBy without judge whether "group by" already exists.
> Finally, I think in this case, the main select and sub-select shouldn't be merged.



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