diff --git a/src/common/src/ttypes.c b/src/common/src/ttypes.c
index a2c16a705fb9d27eae5b131c917a2bf118859b4d..4aee027c0b759aacaf9b1deeb9a3a8e651c33ae1 100644
--- a/src/common/src/ttypes.c
+++ b/src/common/src/ttypes.c
@@ -364,7 +364,7 @@ char tTokenTypeSwitcher[13] = {
 };
 
 bool isValidDataType(int32_t type, int32_t length) {
-  if (type < TSDB_DATA_TYPE_BOOL || type > TSDB_DATA_TYPE_NCHAR) {
+  if (type < TSDB_DATA_TYPE_NULL || type > TSDB_DATA_TYPE_NCHAR) {
     return false;
   }
 
diff --git a/src/inc/tsdb.h b/src/inc/tsdb.h
index 3f3ad8dc9a3d135fcf8bb884d1227d6ec5534762..e8b083ed6bff2a26a7670b166f0f824b4e8b1a8e 100644
--- a/src/inc/tsdb.h
+++ b/src/inc/tsdb.h
@@ -109,8 +109,8 @@ int  tsdbTableSetSName(STableCfg *config, char *sname, bool dup);
 int  tsdbTableSetStreamSql(STableCfg *config, char *sql, bool dup);
 void tsdbClearTableCfg(STableCfg *config);
 
-int32_t    tsdbGetTableTagVal(TsdbRepoT *repo, STableId *id, int32_t colId, int16_t *type, int16_t *bytes, char **val);
-char *     tsdbGetTableName(TsdbRepoT *repo, const STableId *id, int16_t *bytes);
+void* tsdbGetTableTagVal(TsdbRepoT* repo, const STableId* id, int32_t colId, int16_t type, int16_t bytes);
+char* tsdbGetTableName(TsdbRepoT *repo, const STableId *id);
 STableCfg *tsdbCreateTableCfgFromMsg(SMDCreateTableMsg *pMsg);
 
 int   tsdbCreateTable(TsdbRepoT *repo, STableCfg *pCfg);
diff --git a/src/query/src/qExecutor.c b/src/query/src/qExecutor.c
index efa320f544ffdde861b6455ac245f7b557b5192d..2c22a28d348e09807d1b00b8096d5967a5adf674 100644
--- a/src/query/src/qExecutor.c
+++ b/src/query/src/qExecutor.c
@@ -2224,24 +2224,26 @@ static int64_t doScanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
  * set tag value in SQLFunctionCtx
  * e.g.,tag information into input buffer
  */
-static void doSetTagValueInParam(void *tsdb, STableId* pTableId, int32_t tagColId, tVariant *param) {
-  tVariantDestroy(param);
-
-  char *  val = NULL;
-  int16_t bytes = 0;
-  int16_t type = 0;
+static void doSetTagValueInParam(void *tsdb, STableId* pTableId, int32_t tagColId, tVariant *tag, int16_t type,
+    int16_t bytes) {
+  tVariantDestroy(tag);
 
   if (tagColId == TSDB_TBNAME_COLUMN_INDEX) {
-    val = tsdbGetTableName(tsdb, pTableId, &bytes);
-    type = TSDB_DATA_TYPE_BINARY;
-    tVariantCreateFromBinary(param, varDataVal(val), varDataLen(val), type);
+    char* val = tsdbGetTableName(tsdb, pTableId);
+    assert(val != NULL);
+    
+    tVariantCreateFromBinary(tag, varDataVal(val), varDataLen(val), TSDB_DATA_TYPE_BINARY);
   } else {
-    tsdbGetTableTagVal(tsdb, pTableId, tagColId, &type, &bytes, &val);
+    char* val = tsdbGetTableTagVal(tsdb, pTableId, tagColId, type, bytes);
+    if (val == NULL) {
+      tag->nType = TSDB_DATA_TYPE_NULL;
+      return;
+    }
     
     if (type == TSDB_DATA_TYPE_BINARY || type == TSDB_DATA_TYPE_NCHAR) {
-      tVariantCreateFromBinary(param, varDataVal(val), varDataLen(val), type);
+      tVariantCreateFromBinary(tag, varDataVal(val), varDataLen(val), type);
     } else {
-      tVariantCreateFromBinary(param, val, bytes, type);
+      tVariantCreateFromBinary(tag, val, bytes, type);
     }
   }
 }
@@ -2249,25 +2251,29 @@ static void doSetTagValueInParam(void *tsdb, STableId* pTableId, int32_t tagColI
 void setTagVal(SQueryRuntimeEnv *pRuntimeEnv, STableId* pTableId, void *tsdb) {
   SQuery *pQuery = pRuntimeEnv->pQuery;
 
-  SSqlFuncMsg *pFuncMsg = &pQuery->pSelectExpr[0].base;
-  if (pQuery->numOfOutput == 1 && pFuncMsg->functionId == TSDB_FUNC_TS_COMP) {
-    assert(pFuncMsg->numOfParams == 1);
-    doSetTagValueInParam(tsdb, pTableId, pFuncMsg->arg->argValue.i64, &pRuntimeEnv->pCtx[0].tag);
+  SExprInfo *pExprInfo = &pQuery->pSelectExpr[0];
+  if (pQuery->numOfOutput == 1 && pExprInfo->base.functionId == TSDB_FUNC_TS_COMP) {
+  
+    assert(pExprInfo->base.numOfParams == 1);
+    doSetTagValueInParam(tsdb, pTableId, pExprInfo->base.arg->argValue.i64, &pRuntimeEnv->pCtx[0].tag,
+                         pExprInfo->type, pExprInfo->bytes);
   } else {
     // set tag value, by which the results are aggregated.
     for (int32_t idx = 0; idx < pQuery->numOfOutput; ++idx) {
-      SColIndex *pCol = &pQuery->pSelectExpr[idx].base.colInfo;
-
+      SExprInfo* pExprInfo = &pQuery->pSelectExpr[idx];
+  
       // ts_comp column required the tag value for join filter
-      if (!TSDB_COL_IS_TAG(pCol->flag)) {
+      if (!TSDB_COL_IS_TAG(pExprInfo->base.colInfo.flag)) {
         continue;
       }
 
       // todo use tag column index to optimize performance
-      doSetTagValueInParam(tsdb, pTableId, pCol->colId, &pRuntimeEnv->pCtx[idx].tag);
+      doSetTagValueInParam(tsdb, pTableId, pExprInfo->base.colInfo.colId, &pRuntimeEnv->pCtx[idx].tag,
+          pExprInfo->type, pExprInfo->bytes);
     }
 
     // set the join tag for first column
+    SSqlFuncMsg *pFuncMsg = &pExprInfo->base;
     if (pFuncMsg->functionId == TSDB_FUNC_TS && pFuncMsg->colInfo.colIndex == PRIMARYKEY_TIMESTAMP_COL_INDEX &&
         pRuntimeEnv->pTSBuf != NULL) {
       assert(pFuncMsg->numOfParams == 1);
@@ -6005,7 +6011,7 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
   num = taosArrayGetSize(pa);
 
   assert(num == pQInfo->groupInfo.numOfTables);
-  int16_t type, bytes;
+//  int16_t type, bytes;
 
   int32_t functionId = pQuery->pSelectExpr[0].base.functionId;
   if (functionId == TSDB_FUNC_TID_TAG) { // return the tags & table Id
@@ -6013,7 +6019,6 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
     SExprInfo* pExprInfo = &pQuery->pSelectExpr[0];
 
     int32_t rsize = pExprInfo->bytes;
-    char* data = NULL;
 
     for(int32_t i = 0; i < num; ++i) {
       SGroupItem* item = taosArrayGet(pa, i);
@@ -6031,8 +6036,25 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
       *(int32_t*) output = pQInfo->vgId;
       output += sizeof(pQInfo->vgId);
 
-      tsdbGetTableTagVal(pQInfo->tsdb, &item->id, pExprInfo->base.colInfo.colId, &type, &bytes, &data);
-      memcpy(output, data, bytes);
+      int16_t bytes = pExprInfo->bytes;
+      int16_t type = pExprInfo->type;
+      
+      char* val = tsdbGetTableTagVal(pQInfo->tsdb, &item->id, pExprInfo->base.colInfo.colId, type, bytes);
+      
+      // todo refactor
+      if (type == TSDB_DATA_TYPE_BINARY || type == TSDB_DATA_TYPE_NCHAR) {
+        if (val == NULL) {
+          setVardataNull(output, type);
+        } else {
+          memcpy(output, val, varDataTLen(val));
+        }
+      } else {
+        if (val == NULL) {
+          setNull(output, type, bytes);
+        } else {
+          memcpy(output, val, bytes);
+        }
+      }
     }
 
     qTrace("QInfo:%p create (tableId, tag) info completed, rows:%d", pQInfo, num);
@@ -6041,17 +6063,18 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
       SExprInfo* pExprInfo = pQuery->pSelectExpr;
       SGroupItem* item = taosArrayGet(pa, i);
 
-      char* data = NULL;
       for(int32_t j = 0; j < pQuery->numOfOutput; ++j) {
         // todo check the return value, refactor codes
         if (pExprInfo[j].base.colInfo.colId == TSDB_TBNAME_COLUMN_INDEX) {
-          data = tsdbGetTableName(pQInfo->tsdb, &item->id, &bytes);
+          char* data = tsdbGetTableName(pQInfo->tsdb, &item->id);
           
           char* dst = pQuery->sdata[j]->data + i * (TSDB_TABLE_NAME_LEN + VARSTR_HEADER_SIZE);
           memcpy(dst, data, varDataTLen(data));
-        } else {// todo refactor, return the true length of binary|nchar data
-          tsdbGetTableTagVal(pQInfo->tsdb, &item->id, pExprInfo[j].base.colInfo.colId, &type, &bytes, &data);
-          assert(bytes <= pExprInfo[j].bytes && type == pExprInfo[j].type);
+        } else {// todo refactor
+          int16_t type = pExprInfo[j].type;
+          int16_t bytes = pExprInfo[j].bytes;
+          
+          char* data = tsdbGetTableTagVal(pQInfo->tsdb, &item->id, pExprInfo[j].base.colInfo.colId, type, bytes);
           
           char* dst = pQuery->sdata[j]->data + i * pExprInfo[j].bytes;
           if (type == TSDB_DATA_TYPE_BINARY || type == TSDB_DATA_TYPE_NCHAR) {
diff --git a/src/tsdb/src/tsdbMeta.c b/src/tsdb/src/tsdbMeta.c
index 5e8412a1ec98d96252c93a466b76de4e0a198737..0a7f811511090bc708ee4e1feb0fce467cec75d3 100644
--- a/src/tsdb/src/tsdbMeta.c
+++ b/src/tsdb/src/tsdbMeta.c
@@ -260,45 +260,33 @@ STSchema * tsdbGetTableTagSchema(STsdbMeta *pMeta, STable *pTable) {
   }
 }
 
-int32_t tsdbGetTableTagVal(TsdbRepoT* repo, STableId* id, int32_t colId, int16_t* type, int16_t* bytes, char** val) {
+void* tsdbGetTableTagVal(TsdbRepoT* repo, const STableId* id, int32_t colId, int16_t type, int16_t bytes) {
   STsdbMeta* pMeta = tsdbGetMeta(repo);
   STable* pTable = tsdbGetTableByUid(pMeta, id->uid);
 
   STSchema *pSchema = tsdbGetTableTagSchema(pMeta, pTable);
   STColumn *pCol = tdGetColOfID(pSchema, colId);
   if (pCol == NULL) {
-    return -1; // No matched tag volumn
+    return NULL;  // No matched tag volumn
   }
   
-  *val = tdGetKVRowValOfCol(pTable->tagVal, colId);
-  *type = pCol->type;
+  char* val = tdGetKVRowValOfCol(pTable->tagVal, colId);
+  assert(type == pCol->type && bytes == pCol->bytes);
   
-  if (*val != NULL) {
-    if (IS_VAR_DATA_TYPE(*type)) {
-      *bytes = varDataLen(*val);
-    } else {
-      *bytes = TYPE_BYTES[*type];
-    }
+  if (val != NULL && IS_VAR_DATA_TYPE(type)) {
+    assert(varDataLen(val) < pCol->bytes);
   }
   
-  return TSDB_CODE_SUCCESS;
+  return val;
 }
 
-char* tsdbGetTableName(TsdbRepoT *repo, const STableId* id, int16_t* bytes) {
+char* tsdbGetTableName(TsdbRepoT *repo, const STableId* id) {
   STsdbMeta* pMeta = tsdbGetMeta(repo);
   STable* pTable = tsdbGetTableByUid(pMeta, id->uid);
   
   if (pTable == NULL) {
-    if (bytes != NULL) {
-      *bytes = 0;
-    }
-    
     return NULL;
   } else {
-    if (bytes != NULL) {
-      *bytes = varDataLen(pTable->name);
-    }
-    
     return (char*) pTable->name;
   }
 }