From 477943c6098d153a80977ed8151bac4c0626bb2a Mon Sep 17 00:00:00 2001
From: cqliang1995 <cq.liang@outlook.com>
Date: Wed, 17 May 2023 08:16:49 +0000
Subject: [PATCH] fix string type null value error in dblink.

---
 deps/oblib/src/common/object/ob_obj_funcs.h | 6 +++++-
 deps/oblib/src/common/object/ob_object.h    | 3 ++-
 src/sql/engine/dml/ob_link_op.cpp           | 4 ++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/deps/oblib/src/common/object/ob_obj_funcs.h b/deps/oblib/src/common/object/ob_obj_funcs.h
index 7130d4b289..9d51601313 100644
--- a/deps/oblib/src/common/object/ob_obj_funcs.h
+++ b/deps/oblib/src/common/object/ob_obj_funcs.h
@@ -97,7 +97,11 @@ template <>
   UNUSED(obj);
   UNUSED(params);
   int ret = OB_SUCCESS;
-  ret = databuff_printf(buffer, length, pos, "NULL");
+  if (params.print_null_string_value_) {
+    ret = databuff_printf(buffer, length, pos, "''");
+  } else {
+    ret = databuff_printf(buffer, length, pos, "NULL");
+  }
   return ret;
 }
 template <>
diff --git a/deps/oblib/src/common/object/ob_object.h b/deps/oblib/src/common/object/ob_object.h
index 86468dbffd..621dd83a6d 100644
--- a/deps/oblib/src/common/object/ob_object.h
+++ b/deps/oblib/src/common/object/ob_object.h
@@ -1115,7 +1115,8 @@ struct ObObjPrintParams
       uint32_t binary_string_print_hex_:1;
       uint32_t need_print_converter_:1;
       uint32_t print_const_expr_type_:1;
-      uint32_t reserved_:23;
+      uint32_t print_null_string_value_:1;
+      uint32_t reserved_:22;
     };
   };
 
diff --git a/src/sql/engine/dml/ob_link_op.cpp b/src/sql/engine/dml/ob_link_op.cpp
index fc5f265f94..bcb7fb8c54 100644
--- a/src/sql/engine/dml/ob_link_op.cpp
+++ b/src/sql/engine/dml/ob_link_op.cpp
@@ -240,6 +240,10 @@ int ObLinkOp::combine_link_stmt(const ObString &link_stmt_fmt,
       int64_t param_idx = param_infos.at(next_param).idx_;
       const ObObjParam &param = param_store.at(param_idx);
       ObObjPrintParams obj_print_params = CREATE_OBJ_PRINT_PARAM(ctx_.get_my_session());
+
+      if (lib::is_oracle_mode() && ObSQLUtils::is_oracle_empty_string(param)) {
+        obj_print_params.print_null_string_value_  = true;
+      }
       if (DBLINK_DRV_OCI == link_type_) {
         // Ensure that when oceanbase connects to oracle,
         // the target character set of param is the same as that of oci connection.