diff --git a/include/client/taos.h b/include/client/taos.h
index 111cd8ad3b5cff9add9e03574c08b008775431e6..792037aaa7ed5369e8d48f35a4d697ec91ee6a8b 100644
--- a/include/client/taos.h
+++ b/include/client/taos.h
@@ -188,7 +188,7 @@ DLL_EXPORT bool        taos_is_null(TAOS_RES *res, int32_t row, int32_t col);
 DLL_EXPORT bool        taos_is_update_query(TAOS_RES *res);
 DLL_EXPORT int         taos_fetch_block(TAOS_RES *res, TAOS_ROW *rows);
 DLL_EXPORT int         taos_validate_sql(TAOS *taos, const char *sql);
-DLL_EXPORT void taos_reset_current_db(TAOS *taos);
+DLL_EXPORT void        taos_reset_current_db(TAOS *taos);
 
 DLL_EXPORT int *taos_fetch_lengths(TAOS_RES *res);
 DLL_EXPORT TAOS_ROW *taos_result_block(TAOS_RES *res);
diff --git a/source/client/inc/clientInt.h b/source/client/inc/clientInt.h
index e930dc2675fc55ce40ab408d14be22b80e07326f..0749ce9e7dd6bcfdd7b25d9a5eb629c5a56cea0b 100644
--- a/source/client/inc/clientInt.h
+++ b/source/client/inc/clientInt.h
@@ -136,7 +136,7 @@ typedef struct STscObj {
   uint32_t        connId;
   int32_t         connType;
   uint64_t        id;         // ref ID returned by taosAddRef
-  TdThreadMutex mutex;      // used to protect the operation on db
+  TdThreadMutex   mutex;      // used to protect the operation on db
   int32_t         numOfReqs;  // number of sqlObj bound to this connection
   SAppInstInfo*   pAppInfo;
 } STscObj;
@@ -152,7 +152,7 @@ typedef struct SResultColumn {
 typedef struct SReqResultInfo {
   const char*    pRspMsg;
   const char*    pData;
-  TAOS_FIELD*    fields;
+  TAOS_FIELD*    fields;     // todo, column names are not needed.
   TAOS_FIELD*    userFields; // the fields info that return to user
   uint32_t       numOfCols;
   int32_t*       length;
@@ -222,6 +222,7 @@ void  destroyRequest(SRequestObj* pRequest);
 
 char* getDbOfConnection(STscObj* pObj);
 void  setConnectionDB(STscObj* pTscObj, const char* db);
+void  resetConnectDB(STscObj* pTscObj);
 
 void taos_init_imp(void);
 int  taos_options_imp(TSDB_OPTION option, const char* str);
diff --git a/source/client/src/clientImpl.c b/source/client/src/clientImpl.c
index 4b41785d0802cb1054732c5bf3fc91053e2fb130..4e68b5331ff9653502e5256f66200a8c4bb75da8 100644
--- a/source/client/src/clientImpl.c
+++ b/source/client/src/clientImpl.c
@@ -56,7 +56,7 @@ TAOS* taos_connect_internal(const char* ip, const char* user, const char* pass,
   }
 
   char localDb[TSDB_DB_NAME_LEN] = {0};
-  if (db != NULL) {
+  if (db != NULL && strlen(db) > 0) {
     if (!validateDbName(db)) {
       terrno = TSDB_CODE_TSC_INVALID_DB_LENGTH;
       return NULL;
@@ -164,6 +164,7 @@ int32_t parseSql(SRequestObj* pRequest, bool topicQuery, SQuery** pQuery) {
     if ((*pQuery)->haveResultSet) {
       setResSchemaInfo(&pRequest->body.resInfo, (*pQuery)->pResSchema, (*pQuery)->numOfResCols);
     }
+
     TSWAP(pRequest->dbList, (*pQuery)->pDbList, SArray*);
     TSWAP(pRequest->tableList, (*pQuery)->pTableList, SArray*);
   }
@@ -803,6 +804,16 @@ void setConnectionDB(STscObj* pTscObj, const char* db) {
   taosThreadMutexUnlock(&pTscObj->mutex);
 }
 
+void resetConnectDB(STscObj* pTscObj) {
+  if (pTscObj == NULL) {
+    return;
+  }
+
+  taosThreadMutexLock(&pTscObj->mutex);
+  pTscObj->db[0] = 0;
+  taosThreadMutexUnlock(&pTscObj->mutex);
+}
+
 int32_t setQueryResultFromRsp(SReqResultInfo* pResultInfo, const SRetrieveTableRsp* pRsp) {
   assert(pResultInfo != NULL && pRsp != NULL);
 
diff --git a/source/client/src/clientMain.c b/source/client/src/clientMain.c
index 2dd77b7f22f9a95559911b1a606620a0f68b80f1..0ca6169883b74398af387d0a25f075f41e8be58a 100644
--- a/source/client/src/clientMain.c
+++ b/source/client/src/clientMain.c
@@ -365,8 +365,7 @@ bool taos_is_null(TAOS_RES *res, int32_t row, int32_t col) {
 }
 
 bool taos_is_update_query(TAOS_RES *res) {
-  // TODO
-  return true;
+  return taos_num_fields(res) == 0;
 }
 
 int taos_fetch_block(TAOS_RES *res, TAOS_ROW *rows) {
@@ -393,8 +392,11 @@ int taos_fetch_block(TAOS_RES *res, TAOS_ROW *rows) {
 int taos_validate_sql(TAOS *taos, const char *sql) { return true; }
 
 void taos_reset_current_db(TAOS *taos) {
-  // TODO
-  return;
+  if (taos == NULL) {
+    return;
+  }
+
+  resetConnectDB(taos);
 }
 
 const char *taos_get_server_info(TAOS *taos) {