comphead commented on issue #6139:
URL:
https://github.com/apache/arrow-datafusion/issues/6139#issuecomment-1536917297
@alamb @jackwener may I ask your help? I have found why projection is not
correct. push_down_projection never called for query like that
```
select 1 a group by a union all select 2 b
```
However its called for
```
select 1 a group by a union select 2 b
```
The reason for that UNION has another logical plan
UNION
```
| logical_plan | Aggregate: groupBy=[[a]], aggr=[[]]
|
| | Union
|
| | Projection: Int64(1) AS a
|
| | Aggregate: groupBy=[[Int64(1)]], aggr=[[]]
|
| | EmptyRelation
|
| | Projection: Int64(2) AS a
|
| | EmptyRelation
```
UNION ALL
```
| logical_plan | Union
|
| | Projection: Int64(1) AS a
|
| | Aggregate: groupBy=[[Int64(1)]], aggr=[[]]
|
| | EmptyRelation
|
| | Projection: Int64(2) AS b
|
| | EmptyRelation
```
UNION have a weird top Aggregate node, which looks strange for me. as
Aggregation happens twice in that case, but because of that UNION
push_down_projection works.
I'm trying to understand the real rootcause if it in bad plan generated in
the first place or bug in push_down_projection
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