mapleFU commented on issue #37840:
URL: https://github.com/apache/arrow/issues/37840#issuecomment-1734797119
@bkietz I found a problem, when `UnifySchemas` called, it calles
`SchemaBuilder::AddField`, when schema has same name, it has conflict solving
options, when using `CONFLICT_MERGE`, it will call `Field::MergeWith`:
```c++
Result<std::shared_ptr<Field>> Field::MergeWith(const Field& other,
MergeOptions options) const {
if (name() != other.name()) {
return Status::Invalid("Field ", name(), " doesn't have the same name as
",
other.name());
}
if (Equals(other, /*check_metadata=*/false)) {
return Copy();
}
if (options.promote_nullability) {
if (type()->Equals(other.type())) {
return Copy()->WithNullable(nullable() || other.nullable());
}
std::shared_ptr<Field> promoted = MaybePromoteNullTypes(*this, other);
if (promoted) return promoted;
}
return Status::Invalid("Unable to merge: Field ", name(),
" has incompatible types: ", type()->ToString(), "
vs ",
other.type()->ToString());
}
```
In this case, if we don't set explicit schema, and deduce by parquets, it
will says `string` and `large_string` is not compatible and failed. Would this
better having a Common type here? Or this case is expected ?
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