feiniaofeiafei opened a new pull request, #65025:
URL: https://github.com/apache/doris/pull/65025
### What problem does this PR solve?
Issue Number: None
Related PR: #31811
Problem Summary:
A nested aggregate query could return incorrect results when multiple outer
group-by aliases referenced the same inner grouping expression.
For example, after resolving aliases, the inner grouping keys were `(a, b)`
while the outer grouping keys became `(a, a)`. `MergeAggregate` determined
whether the groupings were identical by comparing their list sizes. Since both
lists contained two elements, it incorrectly considered them equivalent.
This allowed `SUM(COUNT(DISTINCT c))` to be merged into `COUNT(DISTINCT c)`
while removing grouping key `b`. Values repeated across different `b` groups
were consequently counted only once, producing an undercount.
This change compares the unique grouping-expression sets after projection
replacement. Aggregate layers containing `DISTINCT` are now merged only when
their grouping semantics are actually identical.
### Release note
Fix incorrect query results for nested aggregates with duplicate group-by
aliases and DISTINCT aggregate functions.
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [ ] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [ ] No.
- [ ] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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