diff --git a/src/sql/engine/expr/ob_expr_operator.cpp b/src/sql/engine/expr/ob_expr_operator.cpp
index de158c2522..3c872c5d5f 100644
--- a/src/sql/engine/expr/ob_expr_operator.cpp
+++ b/src/sql/engine/expr/ob_expr_operator.cpp
@@ -290,15 +290,16 @@ int OB_INLINE ObExprOperator::cast_operand_type(common::ObObj &res_obj,
       } else if (lib::is_mysql_mode() && ob_is_json(calc_type)) {
         cast_ctx.dest_collation_ = CS_TYPE_UTF8MB4_BIN;
       }
-      // FIXME: (xiaochu) 就地修改obj类型算法没问题吧?
-      ObObj res_obj_copy = res_obj;
+      ObObj tmp_obj;
       cast_ctx.expect_obj_collation_ = cast_ctx.dest_collation_;
       if (OB_FAIL(ObObjCaster::to_type(res_type.get_calc_type(),
           cast_ctx,
-          res_obj_copy,
-          res_obj))) {
+          res_obj,
+          tmp_obj))) {
         LOG_WARN("fail to convert type", K(ret),
             K(res_type.get_calc_type()), K(res_obj));
+      } else {
+        res_obj = tmp_obj;
       }
       if (OB_SUCC(ret)
           && ob_is_string_or_lob_type(param_type)