diff --git a/src/query/src/qExecutor.c b/src/query/src/qExecutor.c
index cf13ace11f81c79517d4f2e10e3b4647c3bf75ee..6dba5cbd2a2f0501a8144ea14da818e88ab1985a 100644
--- a/src/query/src/qExecutor.c
+++ b/src/query/src/qExecutor.c
@@ -2236,6 +2236,27 @@ static void ensureOutputBuffer(SQueryRuntimeEnv* pRuntimeEnv, SDataBlockInfo* pB
   }
 }
 
+static void doSetInitialTimewindow(SQueryRuntimeEnv* pRuntimeEnv, SDataBlockInfo* pBlockInfo) {
+  SQuery* pQuery = pRuntimeEnv->pQuery;
+
+  if (QUERY_IS_INTERVAL_QUERY(pQuery) && pRuntimeEnv->windowResInfo.prevSKey == TSKEY_INITIAL_VAL) {
+    STimeWindow w = TSWINDOW_INITIALIZER;
+    SWindowResInfo *pWindowResInfo = &pRuntimeEnv->windowResInfo;
+
+    if (QUERY_IS_ASC_QUERY(pQuery)) {
+      getAlignQueryTimeWindow(pQuery, pBlockInfo->window.skey, pBlockInfo->window.skey, pQuery->window.ekey, &w);
+      pWindowResInfo->startTime = w.skey;
+      pWindowResInfo->prevSKey = w.skey;
+    } else {
+      // the start position of the first time window in the endpoint that spreads beyond the queried last timestamp
+      getAlignQueryTimeWindow(pQuery, pBlockInfo->window.ekey, pQuery->window.ekey, pBlockInfo->window.ekey, &w);
+
+      pWindowResInfo->startTime = pQuery->window.skey;
+      pWindowResInfo->prevSKey = w.skey;
+    }
+  }
+}
+
 static int64_t doScanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
   SQuery *pQuery = pRuntimeEnv->pQuery;
   STableQueryInfo* pTableQueryInfo = pQuery->current;
@@ -2263,24 +2284,7 @@ static int64_t doScanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
     }
 
     tsdbRetrieveDataBlockInfo(pQueryHandle, &blockInfo);
-
-    // todo extract methods
-    if (QUERY_IS_INTERVAL_QUERY(pQuery) && pRuntimeEnv->windowResInfo.prevSKey == TSKEY_INITIAL_VAL) {
-      STimeWindow w = TSWINDOW_INITIALIZER;
-      SWindowResInfo *pWindowResInfo = &pRuntimeEnv->windowResInfo;
-
-      if (QUERY_IS_ASC_QUERY(pQuery)) {
-        getAlignQueryTimeWindow(pQuery, blockInfo.window.skey, blockInfo.window.skey, pQuery->window.ekey, &w);
-        pWindowResInfo->startTime = w.skey;
-        pWindowResInfo->prevSKey = w.skey;
-      } else {
-        // the start position of the first time window in the endpoint that spreads beyond the queried last timestamp
-        getAlignQueryTimeWindow(pQuery, blockInfo.window.ekey, pQuery->window.ekey, blockInfo.window.ekey, &w);
-
-        pWindowResInfo->startTime = pQuery->window.skey;
-        pWindowResInfo->prevSKey = w.skey;
-      }
-    }
+    doSetInitialTimewindow(pRuntimeEnv, &blockInfo);
 
     // in case of prj/diff query, ensure the output buffer is sufficient to accommodate the results of current block
     ensureOutputBuffer(pRuntimeEnv, &blockInfo);
@@ -2314,7 +2318,6 @@ static int64_t doScanAllDataBlocks(SQueryRuntimeEnv *pRuntimeEnv) {
   if (QUERY_IS_INTERVAL_QUERY(pQuery) && IS_MASTER_SCAN(pRuntimeEnv)) {
     if (Q_STATUS_EQUAL(pQuery->status, QUERY_COMPLETED)) {
       closeAllTimeWindow(&pRuntimeEnv->windowResInfo);
-//      removeRedundantWindow(&pRuntimeEnv->windowResInfo, pTableQueryInfo->lastKey - step, step);
       pRuntimeEnv->windowResInfo.curIndex = pRuntimeEnv->windowResInfo.size - 1;  // point to the last time window
     } else {
       assert(Q_STATUS_EQUAL(pQuery->status, QUERY_RESBUF_FULL));
@@ -3223,6 +3226,13 @@ static void setEnvBeforeReverseScan(SQueryRuntimeEnv *pRuntimeEnv, SQueryStatusI
   SWAP(pQuery->window.skey, pQuery->window.ekey, TSKEY);
 
   SWITCH_ORDER(pQuery->order.order);
+
+  if (QUERY_IS_ASC_QUERY(pQuery)) {
+    assert(pQuery->window.skey <= pQuery->window.ekey);
+  } else {
+    assert(pQuery->window.skey >= pQuery->window.ekey);
+  }
+
   SET_REVERSE_SCAN_FLAG(pRuntimeEnv);
 
   STsdbQueryCond cond = {
@@ -3262,8 +3272,7 @@ static void clearEnvAfterReverseScan(SQueryRuntimeEnv *pRuntimeEnv, SQueryStatus
 
   SET_MASTER_SCAN_FLAG(pRuntimeEnv);
 
-  // update the pQuery->window.skey and pQuery->window.ekey to limit the scan scope of sliding query
-  // during reverse scan
+  // update the pQuery->window.skey and pQuery->window.ekey to limit the scan scope of sliding query during reverse scan
   pTableQueryInfo->lastKey = pStatus->lastKey;
   pQuery->status = pStatus->status;
   
@@ -3289,7 +3298,12 @@ void scanOneTableDataBlocks(SQueryRuntimeEnv *pRuntimeEnv, TSKEY start) {
 
     if (pRuntimeEnv->scanFlag == MASTER_SCAN) {
       qstatus.status = pQuery->status;
-      qstatus.curWindow.ekey = pTableQueryInfo->lastKey - step;
+
+      // do nothing if no data blocks are found qualified during scan
+      if (qstatus.lastKey != pTableQueryInfo->lastKey) {
+        qstatus.curWindow.ekey = pTableQueryInfo->lastKey - step;
+      }
+
       qstatus.lastKey = pTableQueryInfo->lastKey;
     }
 
@@ -6282,7 +6296,7 @@ void qTableQuery(qinfo_t qinfo) {
   SQueryRuntimeEnv* pRuntimeEnv = &pQInfo->runtimeEnv;
   if (onlyQueryTags(pQInfo->runtimeEnv.pQuery)) {
     assert(pQInfo->runtimeEnv.pQueryHandle == NULL);
-    buildTagQueryResult(pQInfo);   // todo support the limit/offset
+    buildTagQueryResult(pQInfo);
   } else if (pQInfo->runtimeEnv.stableQuery) {
     stableQueryImpl(pQInfo);
   } else {
@@ -6403,6 +6417,22 @@ int32_t qKillQuery(qinfo_t qinfo) {
   return TSDB_CODE_SUCCESS;
 }
 
+static void doSetTagValueToResultBuf(char* output, const char* val, int16_t type, int16_t bytes) {
+  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 {  // todo here stop will cause client crash
+      memcpy(output, val, bytes);
+    }
+  }
+}
+
 static void buildTagQueryResult(SQInfo* pQInfo) {
   SQueryRuntimeEnv *pRuntimeEnv = &pQInfo->runtimeEnv;
   SQuery *          pQuery = pRuntimeEnv->pQuery;
@@ -6459,25 +6489,11 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
       output += sizeof(pQInfo->vgId);
 
       if (pExprInfo->base.colInfo.colId == TSDB_TBNAME_COLUMN_INDEX) {
-        char *data = tsdbGetTableName(item->pTable);
+        char* data = tsdbGetTableName(item->pTable);
         memcpy(output, data, varDataTLen(data));
       } else {
-        char *val = tsdbGetTableTagVal(item->pTable, 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 {  // todo here stop will cause client crash
-            memcpy(output, val, bytes);
-          }
-        }
+        char* data = tsdbGetTableTagVal(item->pTable, pExprInfo->base.colInfo.colId, type, bytes);
+        doSetTagValueToResultBuf(output, data, type, bytes);
       }
 
       count += 1;
@@ -6494,38 +6510,44 @@ static void buildTagQueryResult(SQInfo* pQInfo) {
   } else {  // return only the tags|table name etc.
     count = 0;
     SSchema tbnameSchema = tGetTableNameColumnSchema();
-    while(pQInfo->tableIndex < num && count < pQuery->rec.capacity) {
+
+    int32_t maxNumOfTables = pQuery->rec.capacity;
+    if (pQuery->limit.limit >= 0 && pQuery->limit.limit < pQuery->rec.capacity) {
+      maxNumOfTables = pQuery->limit.limit;
+    }
+
+    while(pQInfo->tableIndex < num && count < maxNumOfTables) {
       int32_t i = pQInfo->tableIndex++;
 
+      // discard current result due to offset
+      if (pQuery->limit.offset > 0) {
+        pQuery->limit.offset -= 1;
+        continue;
+      }
+
       SExprInfo* pExprInfo = pQuery->pSelectExpr;
       STableQueryInfo* item = taosArrayGetP(pa, i);
 
+      char *data = NULL, *dst = NULL;
+      int16_t type = 0, bytes = 0;
       for(int32_t j = 0; j < pQuery->numOfOutput; ++j) {
+
         if (pExprInfo[j].base.colInfo.colId == TSDB_TBNAME_COLUMN_INDEX) {
-          char* data = tsdbGetTableName(item->pTable);
-          char* dst = pQuery->sdata[j]->data + count * tbnameSchema.bytes;
-          memcpy(dst, data, varDataTLen(data));
-        } else {// todo refactor
-          int16_t type = pExprInfo[j].type;
-          int16_t bytes = pExprInfo[j].bytes;
+          bytes = tbnameSchema.bytes;
+          type = tbnameSchema.type;
+
+          data = tsdbGetTableName(item->pTable);
+          dst = pQuery->sdata[j]->data + count * tbnameSchema.bytes;
+        } else {
+          type = pExprInfo[j].type;
+          bytes = pExprInfo[j].bytes;
           
-          char* data = tsdbGetTableTagVal(item->pTable, pExprInfo[j].base.colInfo.colId, type, bytes);
-          char* dst = pQuery->sdata[j]->data + count * pExprInfo[j].bytes;
+          data = tsdbGetTableTagVal(item->pTable, pExprInfo[j].base.colInfo.colId, type, bytes);
+          dst = pQuery->sdata[j]->data + count * pExprInfo[j].bytes;
 
-          if (type == TSDB_DATA_TYPE_BINARY || type == TSDB_DATA_TYPE_NCHAR) {
-            if (data == NULL) {
-              setVardataNull(dst, type);
-            } else {
-              memcpy(dst, data, varDataTLen(data));
-            }
-          } else {
-            if (data == NULL) {
-              setNull(dst, type, bytes);
-            } else {
-              memcpy(dst, data, pExprInfo[j].bytes);
-            }
-          }
         }
+
+        doSetTagValueToResultBuf(dst, data, type, bytes);
       }
       count += 1;
     }
diff --git a/tests/script/general/parser/first_last_query.sim b/tests/script/general/parser/first_last_query.sim
index fa5ed8b4adfe80386b20470dd64f0e571cea01c5..d11bdccb12066fb0d9249b3117f8b0dc00a5eca5 100644
--- a/tests/script/general/parser/first_last_query.sim
+++ b/tests/script/general/parser/first_last_query.sim
@@ -126,3 +126,14 @@ endi
 if $data01 != 0 then
   return -1
 endi
+
+#add check for out of range first/last query
+sql select first(ts),last(ts) from first_tb4 where ts>'2018-9-18 1:40:01';
+if $row != 0 then
+  return -1
+endi
+
+sql select first(ts),last(ts) from first_tb4 where ts<'2018-9-17 8:50:0';
+if $row != 0 then
+  return -1
+endi
\ No newline at end of file
diff --git a/tests/script/general/parser/null_char.sim b/tests/script/general/parser/null_char.sim
index 09e761c85e68b1bc7a4464901080353936a4d8e5..2e39fc7db2e20f9528c2d62458f3a6a625181c73 100644
--- a/tests/script/general/parser/null_char.sim
+++ b/tests/script/general/parser/null_char.sim
@@ -105,6 +105,21 @@ if $data03 != 1 then
   return -1
 endi
 
+sql select tag1 from st2 limit 20 offset 1
+if $rows != 0 then
+  return -1
+endi
+
+sql select tag1 from st2 limit 10 offset 2
+if $rows != 0 then
+  return -1
+endi
+
+sql select tag1 from st2 limit 0 offset 0
+if $rows != 0 then
+  return -1
+endi
+
 sql create table st3 using mt2 tags (NULL, 'ABC', 103, 'FALSE')
 sql select tag1, tag2, tag3, tag5 from st3
 if $rows != 1 then