nikhilsheoran-db opened a new pull request, #44835:
URL: https://github.com/apache/spark/pull/44835
### What changes were proposed in this pull request?
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- Updated the `ReplaceDeduplicateWithAggregate` implementation to reuse
aliases generated for an attribute.
- Added a unit test to ensure scenarios with duplicate non-grouping keys are
correctly optimized.
### Why are the changes needed?
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- `ReplaceDeduplicateWithAggregate` replaces `Deduplicate` with an
`Aggregate` operator with grouping expressions for the deduplication keys and
aggregate expressions for the non-grouping keys (to preserve the output schema
and keep the non-grouping columns).
- For non-grouping key `a#X`, it generates an aggregate expression of the
form `first(a#X, false) AS a#Y`
- In case the non-grouping keys have a repeated attribute (with the same
name and exprId), the existing logic would generate two different aggregate
expressions both having two different exprId.
- This then leads to duplicate rewrite attributes error (in
`transformUpWithNewOutput`) when transforming the remaining tree.
- For example, for the query
```
Project [a#0, b#1]
+- Deduplicate [b#1]
+- Project [a#0, a#0, b#1]
+- LocalRelation <empty>, [a#0, b#1]
```
the existing logic would transform it to
```
Project [a#3, b#1]
+- Aggregate [b#1], [first(a#0, false) AS a#3, first(a#0, false) AS a#5, b#1]
+- Project [a#0, a#0, b#1]
+- LocalRelation <empty>, [a#0, b#1]
```
with the aggregate mapping having two entries `a#0 -> a#3, a#0 -> a#5`.
The correct transformation would be
```
Project [a#3, b#1]
+- Aggregate [b#1], [first(a#0, false) AS a#3, first(a#0, false) AS a#3, b#1]
+- Project [a#0, a#0, b#1]
+- LocalRelation <empty>, [a#0, b#1]
```
with the aggregate mapping having only one entry `a#0 -> a#3`.
### Does this PR introduce _any_ user-facing change?
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No
### How was this patch tested?
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Added a unit test in `ResolveOperatorSuite`.
### Was this patch authored or co-authored using generative AI tooling?
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No
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