ike560 opened a new issue, #2938:
URL: https://github.com/apache/arrow-datafusion/issues/2938
**Describe the bug**
Case 1... Exception: Internal error: Impossibly got empty window expression.
This was likely caused by a bug in DataFusion's code.
Case 2... Exception: Schema error（same cause as Case 1 ?）
**To Reproduce**
```py
import datafusion
ctx = datafusion.SessionContext()
datafusion.__version__
```
'0.6.0'
```py
!echo "a,b\n1,4\n2,5\n3,6" > example.csv
ctx.register_csv('example', 'example.csv')
ctx.sql('SELECT * from example').show()
```
+---+---+
| a | b |
+---+---+
| 1 | 4 |
| 2 | 5 |
| 3 | 6 |
+---+---+
Case 1... Exception: Internal error
```py
sql = '''
SELECT AVG(b) AS median_value
FROM (
SELECT
b,
COUNT(b) OVER () AS row_count,
ROW_NUMBER() OVER (ORDER BY b) AS row_number
FROM example
)
ORDER BY median_value
'''
df = ctx.sql(sql)
df.show()
```
Exception Traceback (most recent call last)
Input In [65], in <module>
1 sql = '''
2 SELECT AVG(b) AS median_value
3 FROM (
(...)
10 ORDER BY median_value
11 '''
12 df = ctx.sql(sql)
---> 13 df.show()
Exception: Internal error: Impossibly got empty window expression. This was
likely caused by a bug in DataFusion's code and we would welcome that you file
an bug report in our issue tracker
Case 2... Exception: Schema error
```py
sql = '''
SELECT AVG(b) AS median_value
FROM (
SELECT
b,
COUNT(b) OVER () AS row_count,
ROW_NUMBER() OVER (ORDER BY b) AS row_number
FROM example
)
WHERE row_number IN ((row_count + 1) / 2, (row_count + 2) / 2)
'''
df = ctx.sql(sql)
df.show()
```
Exception Traceback (most recent call last)
Input In [57], in <module>
1 sql = '''
2 SELECT AVG(b) AS median_value
3 FROM (
(...)
10 WHERE row_number IN ((row_count + 1) / 2, (row_count + 2) / 2)
11 '''
12 df = ctx.sql(sql)
---> 13 df.show()
Exception: Schema error: No field named 'row_number'. Valid fields are
'example.b'.
**Additional context**
SQL is meant to be reproduced, and the processing content has no meaning.
I think SQL is correct. Is there a way around it?
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