diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index ae279a8b8b84d54bd1084f668f5594addfbdf11c..f7746debef80db87290550e5865528937b1201a1 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -358,19 +358,28 @@ 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/src/client/src/tscServer.c b/src/client/src/tscServer.c
index 5fbe756b3bd63b0b22bda703ff5b02d4daf82052..dd0975de78dfdc231908130c6a2193d0cbc9f2bf 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -980,7 +980,11 @@ static int32_t serializeSqlExpr(SSqlExpr* pExpr, STableMetaInfo* pTableMetaInfo,
     return TSDB_CODE_TSC_INVALID_OPERATION;
   }
 
-  assert(pExpr->resColId < 0);
+  if (pExpr->resColId >= 0) {
+    tscError("result column id underflowed: %d", pExpr->resColId);
+    return TSDB_CODE_TSC_RES_TOO_MANY;
+  }
+
   SSqlExpr* pSqlExpr = (SSqlExpr *)(*pMsg);
 
   SColIndex* pIndex = &pSqlExpr->colInfo;
diff --git a/src/inc/taoserror.h b/src/inc/taoserror.h
index 0f31b99ac070da2e3c1de0ec8638a7b398bc63a0..43ed20fe14af7c5f60c580dc08ff8456e7903e65 100644
--- a/src/inc/taoserror.h
+++ b/src/inc/taoserror.h
@@ -107,6 +107,7 @@ int32_t* taosGetErrno();
 #define TSDB_CODE_TSC_DUP_COL_NAMES             TAOS_DEF_ERROR_CODE(0, 0x021D)  //"duplicated column names")
 #define TSDB_CODE_TSC_INVALID_TAG_LENGTH        TAOS_DEF_ERROR_CODE(0, 0x021E)  //"Invalid tag length")
 #define TSDB_CODE_TSC_INVALID_COLUMN_LENGTH     TAOS_DEF_ERROR_CODE(0, 0x021F)  //"Invalid column length")
+#define TSDB_CODE_TSC_RES_TOO_MANY              TAOS_DEF_ERROR_CODE(0, 0x0227)  //"Result set too large to be output")
 
 // mnode
 #define TSDB_CODE_MND_MSG_NOT_PROCESSED         TAOS_DEF_ERROR_CODE(0, 0x0300)  //"Message not processed")
diff --git a/src/util/src/terror.c b/src/util/src/terror.c
index 0b9a76004b3e445abe1bbffe593d8061803d1b1b..d1ecc2188bec5c4a5b1af36a67cf177dd6d935ec 100644
--- a/src/util/src/terror.c
+++ b/src/util/src/terror.c
@@ -112,9 +112,10 @@ TAOS_DEFINE_ERROR(TSDB_CODE_TSC_EXCEED_SQL_LIMIT,         "SQL statement too lon
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_FILE_EMPTY,               "File is empty")
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_LINE_SYNTAX_ERROR,        "Syntax error in Line")
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_NO_META_CACHED,           "No table meta cached")
-TAOS_DEFINE_ERROR(TSDB_CODE_TSC_DUP_COL_NAMES,             "duplicated column names")
-TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_TAG_LENGTH,        "Invalid tag length")
-TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_COLUMN_LENGTH,     "Invalid column length")
+TAOS_DEFINE_ERROR(TSDB_CODE_TSC_DUP_COL_NAMES,            "duplicated column names")
+TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_TAG_LENGTH,       "Invalid tag length")
+TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_COLUMN_LENGTH,    "Invalid column length")
+TAOS_DEFINE_ERROR(TSDB_CODE_TSC_RES_TOO_MANY,             "Result set too large to be output")
 
 // mnode
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_MSG_NOT_PROCESSED,        "Message not processed")
diff --git a/tests/pytest/query/unionAllTest.py b/tests/pytest/query/unionAllTest.py
index d1e1bf4d3e11191be2875c464150793936acd065..9a7aedc763db05ebb11da33dc65fa74b2ba8daa3 100644
--- a/tests/pytest/query/unionAllTest.py
+++ b/tests/pytest/query/unionAllTest.py
@@ -103,10 +103,27 @@ class TDTestCase:
                     select count(*) as count, loc from st where ts between 1600000000000 and 1600000000010 group by loc''')
         tdSql.checkRows(6)
 
+        # https://jira.taosdata.com:18080/browse/TS-715
+        tdLog.info("test case for TS-715")
+        sql = ""
+
+        tdSql.execute("create table st2(ts timestamp, c1 int, c2 int, c3 int) tags(loc nchar(20))")
+
+        for i in range(101):
+            if i == 0:
+                sql = "select last(*) from sub0 "
+            else:
+                sql += f"union all select last(*) from sub{i} "
+
+            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))
+
+        tdSql.error(sql)
+
     def stop(self):
         tdSql.close()
         tdLog.success("%s successfully executed" % __file__)
 
 
 tdCases.addWindows(__file__, TDTestCase())
-tdCases.addLinux(__file__, TDTestCase())
\ No newline at end of file
+tdCases.addLinux(__file__, TDTestCase())