diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 0a4b7e9f787dbd01685c2913e513250e46136b4a..b854fd65700a72261a9d7b2fba914562ec55d99d 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -368,19 +368,28 @@ static int32_t handlePassword(SSqlCmd* pCmd, SStrToken* pPwd) {
 // validate the out put field type for "UNION ALL" subclause
 static int32_t normalizeVarDataTypeLength(SSqlCmd* pCmd) {
   const char* msg1 = "columns in select clause not identical";
+  const char* msg2 = "too many select clause siblings, at most 100 allowed";
 
+  int32_t siblings = 0;
   int32_t diffSize = 0;
 
   // if there is only one element, the limit of clause is the limit of global result.
   SQueryInfo* pQueryInfo1 = pCmd->pQueryInfo;
   SQueryInfo* pSibling = pQueryInfo1->sibling;
 
+  // pQueryInfo1 itself
+  ++siblings;
+
   while(pSibling != NULL) {
     int32_t ret = tscFieldInfoCompare(&pQueryInfo1->fieldsInfo, &pSibling->fieldsInfo, &diffSize);
     if (ret != 0) {
       return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg1);
     }
 
+    if (++siblings > 100) {
+      return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg2);
+    }
+
     pSibling = pSibling->sibling;
   }
 
diff --git a/tests/pytest/query/unionAllTest.py b/tests/pytest/query/unionAllTest.py
index cfa7fe568f1a9634b012726984c61bad366f43a7..9a7aedc763db05ebb11da33dc65fa74b2ba8daa3 100644
--- a/tests/pytest/query/unionAllTest.py
+++ b/tests/pytest/query/unionAllTest.py
@@ -109,7 +109,7 @@ class TDTestCase:
 
         tdSql.execute("create table st2(ts timestamp, c1 int, c2 int, c3 int) tags(loc nchar(20))")
 
-        for i in range(7000):
+        for i in range(101):
             if i == 0:
                 sql = "select last(*) from sub0 "
             else:
@@ -118,13 +118,7 @@ class TDTestCase:
             tdSql.execute("create table sub%d using st2 tags('nchar%d')" % (i, i))
             tdSql.execute("insert into sub%d values(%d, %d, %d, %d)" % (i, self.ts + i, i, i, i))
 
-        exception = "Exception(\"ProgrammingError('Result set too large to be output', -2147483097)\")"
-        try:
-            tdSql.query(sql)
-        except Exception as e:
-            if {exception} != {repr(e)}:
-                tdLog.info(f"sql: {sql}, {exception} expected, actually raises {repr(e)}")
-                raise e
+        tdSql.error(sql)
 
     def stop(self):
         tdSql.close()