peter-toth opened a new pull request, #37334:
URL: https://github.com/apache/spark/pull/37334
### What changes were proposed in this pull request?
Keep the output attributes of a `Union` node's first child in the
`RemoveRedundantAliases` rule to avoid correctness issues.
### Why are the changes needed?
To fix the result of the following query:
```
SELECT a, b AS a FROM (
SELECT a, a AS b FROM (SELECT a FROM VALUES (1) AS t(a))
UNION ALL
SELECT a, b FROM (SELECT a, b FROM VALUES (1, 2) AS t(a, b))
)
```
Before this PR the query returns the incorrect result:
```
+---+---+
| a| a|
+---+---+
| 1| 1|
| 2| 2|
+---+---+
```
After this PR it returns the expected result:
```
+---+---+
| a| a|
+---+---+
| 1| 1|
| 1| 2|
+---+---+
```
### Does this PR introduce _any_ user-facing change?
Yes, fixes a correctness issue.
### How was this patch tested?
Added new UTs.
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