universalmind303 opened a new issue, #7481:
URL: https://github.com/apache/arrow-datafusion/issues/7481
### Is your feature request related to a problem or challenge?
if your query contains many nested unions, it could result in an inefficient
plan. If it is a union of unions, we can easily simplify that to a single union
node.
### Describe the solution you'd like
nested union nodes should be rewritten as a single union node
```mermaid
flowchart TD
A[union] --> B[4]
A --> C[union]
C --> D[2]
C --> E[1]
```
```mermaid
flowchart TD
A[union] --> B[4]
A --> D[2]
A --> E[1]
```
### Describe alternatives you've considered
None come to mind.
### Additional context
For reference, polars optimizes these away.
https://github.com/pola-rs/polars/issues/7855
https://github.com/pola-rs/polars/pull/7861
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