alamb commented on code in PR #14384:
URL: https://github.com/apache/datafusion/pull/14384#discussion_r1937555136
##########
datafusion/expr-common/src/type_coercion/binary.rs:
##########
@@ -961,23 +961,31 @@ fn struct_coercion(lhs_type: &DataType, rhs_type:
&DataType) -> Option<DataType>
return None;
}
- let types = std::iter::zip(lhs_fields.iter(), rhs_fields.iter())
+ let coerced_types = std::iter::zip(lhs_fields.iter(),
rhs_fields.iter())
.map(|(lhs, rhs)| comparison_coercion(lhs.data_type(),
rhs.data_type()))
.collect::<Option<Vec<DataType>>>()?;
- let fields = types
+ // preserve the field name and nullability
+ let orig_fields = std::iter::zip(lhs_fields.iter(),
rhs_fields.iter());
+
+ let fields: Vec<FieldRef> = coerced_types
.into_iter()
- .enumerate()
- .map(|(i, datatype)| {
- Arc::new(Field::new(format!("c{i}"), datatype, true))
- })
- .collect::<Vec<FieldRef>>();
+ .zip(orig_fields)
+ .map(|(datatype, (lhs, rhs))| coerce_fields(datatype, lhs,
rhs))
+ .collect();
Some(Struct(fields.into()))
}
_ => None,
}
}
+/// returns the result of coercing two fields to a common type
+fn coerce_fields(common_type: DataType, lhs: &FieldRef, rhs: &FieldRef) ->
FieldRef {
+ let is_nullable = lhs.is_nullable() || rhs.is_nullable();
+ let name = lhs.name(); // pick the name from the left field
Review Comment:
I agree that would be better -- can I do it in a follow on PR?
In my opinion this PR makes things better (doesn't lose field names) even
though it is not perfect and I would like to fix the regression since 43
What I think we should do is switch `comparison_coercion` to use
`type_union_coercion` eventually and then implement the correct coercion there
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