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Posted to github@datafusion.apache.org by "jayzhan211 (via GitHub)" <gi...@apache.org> on 2026/10/18 10:01:59 UTC
[I] `bit_xor` over a sliding window frame returns 0 instead of NULL when the frame has only NULLs [datafusion]
jayzhan211 opened a new issue, #26470:
URL: https://github.com/apache/datafusion/issues/26470
### Describe the bug
When a sliding window frame (one that does not start at `UNBOUNDED PRECEDING`) contains only NULL values, `bit_xor` returns `0` instead of `NULL`. This only happens after the frame has already seen a non-NULL value. The same aggregate over a whole partition returns `NULL` correctly.
### To Reproduce
```sql
SELECT x,
bit_xor(x) OVER (ORDER BY i ROWS BETWEEN CURRENT ROW AND CURRENT ROW) AS sliding,
bit_xor(x) OVER (PARTITION BY i) AS whole
FROM (VALUES (1, 5), (2, NULL), (3, 6)) t(i, x)
ORDER BY i;
```
```
+------+---------+-------+
| x | sliding | whole |
+------+---------+-------+
| 5 | 5 | 5 |
| NULL | 0 | NULL |
| 6 | 6 | 6 |
+------+---------+-------+
```
### Expected behavior
`sliding` is `NULL` on the second row, as in `whole`. DuckDB returns `NULL` there.
### Additional context
`BitXorAccumulator` keeps an `Option` that becomes `Some` on the first non-NULL value. `retract_batch` XORs the leaving values back out, but the state never goes back to `None`. So once every non-NULL value has left the frame, `evaluate` returns `Some(0)`:
https://github.com/apache/datafusion/blob/3470bd0fbc/datafusion/functions-aggregate/src/bit_and_or_xor.rs#L455-L466
One way to fix it is to count the non-NULL values in the frame and return NULL when the count is zero. `avg` had the same kind of problem in #22139.
### Willingness to contribute
Feel free to take it!
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Re: [I] `bit_xor` over a sliding window frame returns 0 instead of NULL when the frame has only NULLs [datafusion]
Posted by "cool9850311 (via GitHub)" <gi...@apache.org>.
cool9850311 commented on issue #26470:
URL: https://github.com/apache/datafusion/issues/26470#issuecomment-6248697385
I'll take it
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Re: [I] `bit_xor` over a sliding window frame returns 0 instead of NULL when the frame has only NULLs [datafusion]
Posted by "jayzhan211 (via GitHub)" <gi...@apache.org>.
jayzhan211 closed issue #26470: `bit_xor` over a sliding window frame returns 0 instead of NULL when the frame has only NULLs
URL: https://github.com/apache/datafusion/issues/26470
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