jayzhan211 commented on code in PR #10221:
URL: https://github.com/apache/datafusion/pull/10221#discussion_r1578683165
##########
datafusion/expr/src/type_coercion/binary.rs:
##########
@@ -643,9 +643,8 @@ fn dictionary_coercion(
Dictionary(_lhs_index_type, lhs_value_type),
Dictionary(_rhs_index_type, rhs_value_type),
) => comparison_coercion(lhs_value_type, rhs_value_type),
- (d @ Dictionary(_, value_type), other_type)
- | (other_type, d @ Dictionary(_, value_type))
- if preserve_dictionaries && value_type.as_ref() == other_type =>
+ (d @ Dictionary(_, _), other_type) | (other_type, d @ Dictionary(_, _))
+ if preserve_dictionaries && can_cast_types(other_type, d) =>
Review Comment:
If I understand correctly, we should check whether `value_type` and
`other_type` are coercible. If yes return the new dict with new value type
`Dict(k, i8) and i64 -> Dict(k, i64)`
`Dict(k, i64) and i8 -> Dict(k, i64)`
Instead of `Some(d.clone())` we should create a new dict with new value type.
And, I think we should use the coerce logic in `comparison_coercion` not
`can_cast_types`, because the logic is not totally the same.
```rust
| (other_type, d @ Dictionary(key_type, value_type))
if preserve_dictionaries &&
comparison_coercion(value_type.as_ref(), other_type).is_some() =>
{
let new_value = comparison_coercion(&value_type,
other_type).unwrap();
Some(DataType::Dictionary(key_type.clone(), Box::new(new_value)))
}
```
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