fix: Specify row count in sort_batch for empty batch (#10094)

Author: viirya

datafusion/physical-plan/src/sorts/sort.rs

@@ -46,7 +46,7 @@ use arrow::datatypes::SchemaRef;
 use arrow::ipc::reader::FileReader;
 use arrow::record_batch::RecordBatch;
 use arrow::row::{RowConverter, SortField};
-use arrow_array::{Array, UInt32Array};
+use arrow_array::{Array, RecordBatchOptions, UInt32Array};
 use arrow_schema::DataType;
 use datafusion_common::{exec_err, DataFusionError, Result};
 use datafusion_common_runtime::SpawnedTask;
@@ -617,7 +617,12 @@ pub(crate) fn sort_batch(
         .map(|c| take(c.as_ref(), &indices, None))
         .collect::<Result<_, _>>()?;
 
-    Ok(RecordBatch::try_new(batch.schema(), columns)?)
+    let options = RecordBatchOptions::new().with_row_count(Some(indices.len()));
+    Ok(RecordBatch::try_new_with_options(
+        batch.schema(),
+        columns,
+        &options,
+    )?)
 }
 
 #[inline]
@@ -1008,6 +1013,8 @@ mod tests {
     use datafusion_execution::config::SessionConfig;
     use datafusion_execution::runtime_env::RuntimeConfig;
 
+    use datafusion_common::ScalarValue;
+    use datafusion_physical_expr::expressions::Literal;
     use futures::FutureExt;
 
     #[tokio::test]
@@ -1415,4 +1422,20 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn test_empty_sort_batch() {
+        let schema = Arc::new(Schema::empty());
+        let options = RecordBatchOptions::new().with_row_count(Some(1));
+        let batch =
+            RecordBatch::try_new_with_options(schema.clone(), vec![], &options).unwrap();
+
+        let expressions = vec![PhysicalSortExpr {
+            expr: Arc::new(Literal::new(ScalarValue::Int64(Some(1)))),
+            options: SortOptions::default(),
+        }];
+
+        let result = sort_batch(&batch, &expressions, None).unwrap();
+        assert_eq!(result.num_rows(), 1);
+    }
 }