Fix but, update tests

Author: alamb

datafusion/expr-common/src/type_coercion/binary.rs

@@ -507,18 +507,19 @@ fn type_union_resolution_coercion(
                 None
             }
 
-            let types = lhs
+            let coerced_types = lhs
                 .iter()
                 .map(|lhs_field| search_corresponding_coerced_type(lhs_field, rhs))
                 .collect::<Option<Vec<_>>>()?;
 
-            let fields = types
+            // preserve the field name and nullability
+            let orig_fields = std::iter::zip(lhs.iter(), rhs.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(DataType::Struct(fields.into()))
         }
         _ => {

datafusion/sqllogictest/test_files/case.slt

@@ -432,7 +432,7 @@ create or replace table t as values
 );
 
 # This case forces all branches to be coerced to the same type
-query error
+query ?
 SELECT
   case
     when column1 > 0 then column2
@@ -441,13 +441,10 @@ SELECT
   end
 FROM t;
 ----
-DataFusion error: type_coercion
-caused by
-Error during planning: Failed to coerce then ([List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8View, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} })]) and else (Some(List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }))) to common types in CASE WHEN expression
-
+[{foo: baz}]
 
 # different orders of the branches
-query error
+query ?
 SELECT
   case
     when column1 > 0 then column3 -- NB different order
@@ -456,10 +453,7 @@ SELECT
   end
 FROM t;
 ----
-DataFusion error: type_coercion
-caused by
-Error during planning: Failed to coerce then ([List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }), List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} })]) and else (Some(List(Field { name: "item", data_type: Struct([Field { name: "foo", data_type: Utf8View, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }]), nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {} }))) to common types in CASE WHEN expression
-
+[{foo: bar}]
 
 # different orders of the branches
 query ?
@@ -471,7 +465,7 @@ SELECT
   end
 FROM t;
 ----
-[{c0: blarg}]
+[{foo: blarg}]