Phoenix500526 opened a new issue, #27074:
URL: https://github.com/apache/datafusion/issues/27074
A filter applied after `GROUP BY` can change the number of rows counted
within a group. Reproduced with DataFusion CLI `57.0.0-dev`:
```sql
SELECT c
FROM (
SELECT a, COUNT(*) AS c
FROM (VALUES (1), (1)) AS t(a)
GROUP BY a
) AS counts
WHERE random() < 0.5;
```
**Expected:** Both input rows belong to the same group. The query should
return either `2` or no rows, depending on whether the group passes the filter.
**Actual:** The query can return `1`. `EXPLAIN VERBOSE` shows that
`push_down_filter` moves `random() < 0.5` below the aggregate, so it runs once
per input row. If exactly one row passes, the count is `1`.
@DKER2 originally reported this behavior for an aggregate without `GROUP
BY`. The example above reproduces it with an ordinary grouping key,
independently of the empty-input behavior tracked in #26545. [Original
comment](https://github.com/apache/datafusion/issues/26545#issuecomment-6540813770)
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