[CP] fix bug for px-coord merge sort

src/sql/engine/px/ob_px_merge_sort_coord.cpp

@@ -33,6 +33,7 @@ using namespace oceanbase::sql;
 using namespace oceanbase::sql::dtl;
 
 OB_SERIALIZE_MEMBER((ObPxMergeSortCoordInput, ObPxReceiveInput));
+OB_SERIALIZE_MEMBER((ObPxMergeSortCoord, ObPxCoord), sort_columns_);
 
 int ObPxMergeSortCoord::ObPxMergeSortCoordEventListener::on_root_data_channel_setup()
 {
@@ -77,6 +78,9 @@ int ObPxMergeSortCoord::inner_open(ObExecContext& ctx) const
     LOG_WARN("fail init fifo allocator", K(ret));
   } else if (OB_FAIL(setup_scheduler(*px_ctx))) {
     LOG_WARN("fail setup scheduler", K(ret));
+  } else if (sort_columns_.empty()) {
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("sort_column could not be empty", K(ret));
   } else {
     px_ctx->row_heap_.set_sort_columns(sort_columns_);
     px_ctx->metric_.set_id(get_id());

src/sql/engine/px/ob_px_merge_sort_coord.h

@@ -81,6 +81,9 @@ private:
 };
 
 class ObPxMergeSortCoord : public ObPxCoord, public ObSortableTrait {
+public:
+  OB_UNIS_VERSION_V(2);
+
 public:
   class ObPxMergeSortCoordCtx;
 

src/sql/executor/ob_fifo_receive.cpp

@@ -1085,6 +1085,9 @@ int ObMergeSortReceive::create_op_ctx(ObExecContext& exec_ctx, ObAsyncReceiveCtx
   } else if (OB_ISNULL(receive_ctx)) {
     ret = OB_ERR_UNEXPECTED;
     LOG_WARN("fail to create merge sort receive ctx", K(ret));
+  } else if (sort_columns_.empty()) {
+    ret = OB_ERR_UNEXPECTED;
+    LOG_WARN("sort_column could not be empty", K(ret));
   } else {
     receive_ctx->row_comparer_.init(sort_columns_, receive_ctx->child_rows_);
     op_ctx = receive_ctx;