zZKato opened a new issue, #9098:
URL: https://github.com/apache/arrow-datafusion/issues/9098
### Describe the bug
When coalescing between two arrays, datafusion will infer the type to be
Utf8.
### To Reproduce
```
❯ select arrow_typeof(coalesce([1], [2]));
+-------------------------------------------------------------------+
| arrow_typeof(coalesce(make_array(Int64(1)),make_array(Int64(2)))) |
+-------------------------------------------------------------------+
| Utf8 |
+-------------------------------------------------------------------+
1 row in set. Query took 0.001 seconds.
❯ select arrow_typeof(coalesce(NULL, [2]));
+---------------------------------------------------+
| arrow_typeof(coalesce(NULL,make_array(Int64(2)))) |
+---------------------------------------------------+
| Utf8 |
+---------------------------------------------------+
1 row in set. Query took 0.001 seconds.
❯ select arrow_typeof(coalesce([1], NULL));
+---------------------------------------------------+
| arrow_typeof(coalesce(make_array(Int64(1)),NULL)) |
+---------------------------------------------------+
| Utf8 |
+---------------------------------------------------+
1 row in set. Query took 0.001 seconds.
```
### Expected behavior
Postgres handles this correctly for example:
```sql
select pg_typeof(coalesce(NULL, array[1,2,3]));
-- pg_typeof
-- integer[]
```
### Additional context
I didn't test this extensively but I think the same is true for struct types
(and by extension maybe all "complex" type?)
If someone comes accross this, I am currently working around this by
replacing the coalesce with a case statement:
```rust
when(col("c1").is_null(), col("c2"))
.otherwise(col("c1"))
.unwrap()
.alias("c1"),
```
This preserves the type of the column.
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