mustafasrepo opened a new issue, #5212:
URL: https://github.com/apache/arrow-datafusion/issues/5212
**Describe the bug**
A clear and concise description of what the bug is.
When I run the query below on postgre
```sql
SELECT c1, c9 FROM aggregate_test_100
UNION ALL
SELECT c1, c3 FROM aggregate_test_100
```
where c9 has type `Bigint` and c3 has type `smallint`. It produces a valid
result. However, when I run the above query on datafusion where c9 has type
`Uint32` and c3 has type `Int8`.
It gives the error `ArrowError(CastError("Can't cast value 1491205016 to
type Int8"))`.
The physical plan of the query above in DataFusion is as follows
```sql
"UnionExec",
" ProjectionExec: expr=[c1@0 as c1, c3@1 as c3]",
" CsvExec: files={1 group:
[[Users/akurmustafa/projects/synnada/arrow-datafusion-tmp/testing/data/csv/aggregate_test_100.csv]]},
has_header=true, limit=None, projection=[c1, c3]",
" ProjectionExec: expr=[c1@0 as c1, CAST(c9@1 AS Int8) as c3]",
" CsvExec: files={1 group:
[[Users/akurmustafa/projects/synnada/arrow-datafusion-tmp/testing/data/csv/aggregate_test_100.csv]]},
has_header=true, limit=None, projection=[c1, c9]",
```
Datafusion coerces the types `Uint32` and `Int8` to `Int8`. For instance we
may choose to upcast types to `Int32` for this specific case.
**To Reproduce**
Steps to reproduce the behavior:
One can run query above
**Expected behavior**
A clear and concise description of what you expected to happen.
I expect above query to work
**Additional context**
Add any other context about the problem here.
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