starocean999 opened a new pull request, #16856:
URL: https://github.com/apache/doris/pull/16856
For performance reason, we want to remove constant column from
groupingExprs. For example:
`select sum(T.A) from T group by T.B, 'xyz'` is equivalent
to `select sum(T.A) from T group by T.B`
We can remove constant column `abc` from groupingExprs.
But there is an exception when all groupingExpr are constant For example:
sql1: `select 'abc' from t group by 'abc'`
is not equivalent to
sql2: `select 'abc' from t`
sql3: `select 'abc', sum(a) from t group by 'abc'`
is not equivalent to
sql4: `select 1, sum(a) from t`
(when t is empty, sql3 returns 0 tuple, sql4 return 1 tuple)
We need to keep some constant columns if all groupingExpr are constant.
Consider sql5 `select a from (select "abc" as a, 'def' as b) T group by b,
a;` if the constant column `a` is in select list, this column should not be
removed. sql5 is transformed to
sql6 `select a from (select "abc" as a, 'def' as b) T group by a;`
# Proposed changes
Issue Number: close #xxx
## Problem summary
Describe your changes.
## Checklist(Required)
* [ ] Does it affect the original behavior
* [ ] Has unit tests been added
* [ ] Has document been added or modified
* [ ] Does it need to update dependencies
* [ ] Is this PR support rollback (If NO, please explain WHY)
## Further comments
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[[email protected]](mailto:[email protected]) by explaining why you
chose the solution you did and what alternatives you considered, etc...
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