diff --git a/source/libs/parser/src/parTranslater.c b/source/libs/parser/src/parTranslater.c
index be3acbcff9..20e986c825 100755
--- a/source/libs/parser/src/parTranslater.c
+++ b/source/libs/parser/src/parTranslater.c
@@ -2243,6 +2243,7 @@ static bool dataTypeEqual(const SDataType* l, const SDataType* r) {
 
 // 0 means equal, 1 means the left shall prevail, -1 means the right shall prevail
 static int32_t dataTypeComp(const SDataType* l, const SDataType* r) {
+  if (l->type == TSDB_DATA_TYPE_NULL) return -1;
   if (l->type != r->type) {
     return 1;
   }
diff --git a/tests/system-test/2-query/union.py b/tests/system-test/2-query/union.py
index cd2432f21b..3a6247e62a 100644
--- a/tests/system-test/2-query/union.py
+++ b/tests/system-test/2-query/union.py
@@ -447,6 +447,18 @@ class TDTestCase:
         tdSql.checkData(0, 0, None)
         tdSql.checkData(1, 0, None)
 
+        sql = "select null union select 1"
+        tdSql.query(sql, queryTimes=1)
+        tdSql.checkRows(2)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, 1)
+
+        sql = "select null union select 'asd'"
+        tdSql.query(sql, queryTimes=1)
+        tdSql.checkRows(2)
+        tdSql.checkData(0, 0, None)
+        tdSql.checkData(1, 0, 'asd')
+
     def stop(self):
         tdSql.close()
         tdLog.success(f"{__file__} successfully executed")