mateuszkj opened a new issue, #2542:
URL: https://github.com/apache/arrow-datafusion/issues/2542
**Describe the bug**
`windowExpr` is removed fro Logical Plan during optimization. Which causes
`Impossibly got empty window expression` error.
**To Reproduce**
```sql
RUST_LOG=debug datafusion-cli
WITH _sample_data AS (
SELECT 1 as a, 'aa' AS b
UNION ALL
SELECT 3 as a, 'aa' AS b
UNION ALL
SELECT 5 as a, 'bb' AS b
UNION ALL
SELECT 7 as a, 'bb' AS b
), _data2 AS (
SELECT
row_number() OVER (PARTITION BY s.b ORDER BY s.a) AS seq,
s.a,
s.b
FROM _sample_data s
)
SELECT d.b, MAX(d.a) AS max_a
FROM _data2 d
GROUP BY d.b
ORDER BY d.b;
-- Result
-- Error: Impossibly got empty window expression
```
**Expected behavior**
With above SQL i should got:
```sql
-- Result
-- aa; 3
-- bb; 7
```
**Additional context**
Input logical plan:
```
Sort: #d.b ASC NULLS LAST
Projection: #d.b, #MAX(d.a) AS max_a
Aggregate: groupBy=[[#d.b]], aggr=[[MAX(#d.a)]]
Projection: #_data2.seq, #_data2.a, #_data2.b, alias=d
Projection: #ROW_NUMBER() PARTITION BY [#s.b] ORDER BY [#s.a ASC
NULLS LAST] AS seq, #s.a, #s.b, alias=_data2
WindowAggr: windowExpr=[[ROW_NUMBER() PARTITION BY [#s.b]
ORDER BY [#s.a ASC NULLS LAST]]]
Projection: #_sample_data.a, #_sample_data.b, alias=s
Union
Projection: Int64(1) AS a, Utf8("aa") AS b
EmptyRelation
Projection: Int64(3) AS a, Utf8("aa") AS b
EmptyRelation
Projection: Int64(5) AS a, Utf8("bb") AS b
EmptyRelation
Projection: Int64(7) AS a, Utf8("bb") AS b
EmptyRelation
```
Optimized logical plan:
```
Sort: #d.b ASC NULLS LAST
Projection: #d.b, #MAX(d.a) AS max_a
Aggregate: groupBy=[[#d.b]], aggr=[[MAX(#d.a)]]
Projection: #_data2.a, #_data2.b, alias=d
Projection: #s.a, #s.b, alias=_data2
WindowAggr: windowExpr=[[]] <-------- Here is empty expression
Projection: #_sample_data.a, #_sample_data.b, alias=s
Union
Projection: Int64(1) AS a, Utf8("aa") AS b
EmptyRelation
Projection: Int64(3) AS a, Utf8("aa") AS b
EmptyRelation
Projection: Int64(5) AS a, Utf8("bb") AS b
EmptyRelation
Projection: Int64(7) AS a, Utf8("bb") AS b
EmptyRelation
```
We can see *windowExpr* is empty after optimization. I have tested this case
on master
('[a825891](https://github.com/apache/arrow-datafusion/commit/a82589100d7b07cb629476a2df7eac002f48b8a0)').
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