[CALCITE-3466] JDBC adapter incorrectly drops GROUP BY clause of sub-query

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.21.0, 1.22.0
• Fix Version/s: 1.22.0
• Component/s: jdbc-adapter
• Labels: pull-request-available
• Assignee: Wang Weidong
• Reporter: Wang Weidong
• Due: 31/Dec/19
• Created: 31/Oct/19 12:03
• Updated: 06/Mar/20 04:33
• Resolved: 14/Jan/20 02:08

Description

While convert RelNode to SqlNode, the "group by" statement in subquery was dropped unexpectedly. For example,
original sql is:

select a, avg(c1) from 
(
    select a,sum(d),b as c1 from t group by b,a
) as t 
group by a

RelNode converted by SqlNode is

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]])

And then convert this RelNode to SqlNode, the sql of SqlNode is like this:

SELECT `A`, AVG(`B`)
FROM `T`
GROUP BY `A`

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.

Issue Links

• links to: GitHub Pull Request #1606