alamb commented on code in PR #18713:
URL: https://github.com/apache/datafusion/pull/18713#discussion_r2554091775
##########
datafusion/optimizer/src/optimize_unions.rs:
##########
@@ -105,6 +105,31 @@ fn extract_plans_from_union(plan: Arc<LogicalPlan>) ->
Vec<LogicalPlan> {
.into_iter()
.map(Arc::unwrap_or_clone)
.collect::<Vec<_>>(),
+ LogicalPlan::Projection(Projection {
Review Comment:
Am I right in understanding this change that it transforms
```
Projection
Union
to
```
Union
Projection
```
(aka it pushes the projection to each input of the union?)
Maybe some comments could help future readers
##########
datafusion/optimizer/src/optimize_unions.rs:
##########
@@ -331,6 +356,27 @@ mod tests {
")
}
+ #[test]
+ fn eliminate_nested_union_in_projection() -> Result<()> {
Review Comment:
Without the change in this PR the test fails like
```
────────────┬───────────────────────────────────────────────────────────────────
1 1 │ Union
2 2 │ Projection: id AS table_id, key, value
3 │- TableScan: table
4 │- Projection: id AS table_id, key, value
5 │- TableScan: table
3 │+ Union
4 │+ TableScan: table
5 │+ TableScan: table
6 6 │ TableScan: table
────────────┴───────────────────────────────────────────────────────────────────
```
In other words, the plan is left as
```
Union
Projection: id AS table_id, key, value
Union
TableScan: table
TableScan: table
TableScan: table
```
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