Do not check schema for equality in concat_batches (#4815)

arrow-select/src/concat.rs

@@ -92,7 +92,12 @@ pub fn concat(arrays: &[&dyn Array]) -> Result<ArrayRef, ArrowError> {
     Ok(make_array(mutable.freeze()))
 }
 
-/// Concatenates `batches` together into a single record batch.
+/// Concatenates `batches` together into a single [`RecordBatch`].
+///
+/// The output batch has the specified `schemas`; The schema of the
+/// input are ignored.
+///
+/// Returns an error if the types of underlying arrays are different.
 pub fn concat_batches<'a>(
     schema: &SchemaRef,
     input_batches: impl IntoIterator<Item = &'a RecordBatch>,
@@ -109,20 +114,6 @@ pub fn concat_batches<'a>(
     if batches.is_empty() {
         return Ok(RecordBatch::new_empty(schema.clone()));
     }
-    if let Some((i, _)) = batches
-        .iter()
-        .enumerate()
-        .find(|&(_, batch)| batch.schema() != *schema)
-    {
-        return Err(ArrowError::InvalidArgumentError(format!(
-            "batches[{i}] schema is different with argument schema.
-            batches[{i}] schema: {:?},
-            argument schema: {:?}
-            ",
-            batches[i].schema(),
-            *schema
-        )));
-    }
     let field_num = schema.fields().len();
     let mut arrays = Vec::with_capacity(field_num);
     for i in 0..field_num {
@@ -648,36 +639,45 @@ mod tests {
     }
 
     #[test]
-    fn concat_record_batches_of_different_schemas() {
-        let schema1 = Arc::new(Schema::new(vec![
-            Field::new("a", DataType::Int32, false),
-            Field::new("b", DataType::Utf8, false),
-        ]));
-        let schema2 = Arc::new(Schema::new(vec![
-            Field::new("c", DataType::Int32, false),
-            Field::new("d", DataType::Utf8, false),
-        ]));
+    fn concat_record_batches_of_different_schemas_but_compatible_data() {
+        let schema1 =
+            Arc::new(Schema::new(vec![Field::new("a", DataType::Int32, false)]));
+        // column names differ
+        let schema2 =
+            Arc::new(Schema::new(vec![Field::new("c", DataType::Int32, false)]));
         let batch1 = RecordBatch::try_new(
             schema1.clone(),
-            vec![
-                Arc::new(Int32Array::from(vec![1, 2])),
-                Arc::new(StringArray::from(vec!["a", "b"])),
-            ],
+            vec![Arc::new(Int32Array::from(vec![1, 2]))],
+        )
+        .unwrap();
+        let batch2 =
+            RecordBatch::try_new(schema2, vec![Arc::new(Int32Array::from(vec![3, 4]))])
+                .unwrap();
+        // concat_batches simply uses the schema provided
+        let batch = concat_batches(&schema1, [&batch1, &batch2]).unwrap();
+        assert_eq!(batch.schema().as_ref(), schema1.as_ref());
+        assert_eq!(4, batch.num_rows());
+    }
+
+    #[test]
+    fn concat_record_batches_of_different_schemas_incompatible_data() {
+        let schema1 =
+            Arc::new(Schema::new(vec![Field::new("a", DataType::Int32, false)]));
+        // column names differ
+        let schema2 = Arc::new(Schema::new(vec![Field::new("a", DataType::Utf8, false)]));
+        let batch1 = RecordBatch::try_new(
+            schema1.clone(),
+            vec![Arc::new(Int32Array::from(vec![1, 2]))],
         )
         .unwrap();
         let batch2 = RecordBatch::try_new(
             schema2,
-            vec![
-                Arc::new(Int32Array::from(vec![3, 4])),
-                Arc::new(StringArray::from(vec!["c", "d"])),
-            ],
+            vec![Arc::new(StringArray::from(vec!["foo", "bar"]))],
         )
         .unwrap();
+
         let error = concat_batches(&schema1, [&batch1, &batch2]).unwrap_err();
-        assert_eq!(
-            error.to_string(),
-            "Invalid argument error: batches[1] schema is different with argument schema.\n            batches[1] schema: Schema { fields: [Field { name: \"c\", data_type: Int32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: \"d\", data_type: Utf8, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} },\n            argument schema: Schema { fields: [Field { name: \"a\", data_type: Int32, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }, Field { name: \"b\", data_type: Utf8, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} }\n            "
-        );
+        assert_eq!(error.to_string(), "Invalid argument error: It is not possible to concatenate arrays of different data types.");
     }
 
     #[test]