diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index e24c063b2e..50c8aa0376 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -914,8 +914,8 @@ static int32_t checkInvalidExprForTimeWindow(SSqlCmd* pCmd, SQueryInfo* pQueryIn
 }
 
 int32_t validateIntervalNode(SSqlObj* pSql, SQueryInfo* pQueryInfo, SSqlNode* pSqlNode) {
+  const char* msg1 = "sliding cannot be used without interval";
   const char* msg2 = "interval cannot be less than 10 ms";
-  const char* msg3 = "sliding cannot be used without interval";
 
   SSqlCmd* pCmd = &pSql->cmd;
 
@@ -924,7 +924,7 @@ int32_t validateIntervalNode(SSqlObj* pSql, SQueryInfo* pQueryInfo, SSqlNode* pS
   
   if (!TPARSER_HAS_TOKEN(pSqlNode->interval.interval)) {
     if (TPARSER_HAS_TOKEN(pSqlNode->sliding)) {
-      return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg3);
+      return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg1);
     }
 
     return TSDB_CODE_SUCCESS;
@@ -945,7 +945,7 @@ int32_t validateIntervalNode(SSqlObj* pSql, SQueryInfo* pQueryInfo, SSqlNode* pS
   if (pQueryInfo->interval.intervalUnit != 'n' && pQueryInfo->interval.intervalUnit != 'y') {
 
     // interval cannot be less than 10 milliseconds
-    if (convertTimePrecision(pQueryInfo->interval.interval, tinfo.precision, TSDB_TIME_PRECISION_MILLI) < tsMinIntervalTime) {
+    if (convertTimePrecision(pQueryInfo->interval.interval, tinfo.precision, TSDB_TIME_PRECISION_MICRO) < tsMinIntervalTime) {
       return invalidOperationMsg(tscGetErrorMsgPayload(pCmd), msg2);
     }
   }
diff --git a/src/common/src/tglobal.c b/src/common/src/tglobal.c
index 51d44add4c..ec98915227 100644
--- a/src/common/src/tglobal.c
+++ b/src/common/src/tglobal.c
@@ -84,8 +84,8 @@ int32_t tsMaxNumOfOrderedResults = 100000;
 // 10 ms for sliding time, the value will changed in case of time precision changed
 int32_t tsMinSlidingTime = 10;
 
-// 10 ms for interval time range, changed accordingly
-int32_t tsMinIntervalTime = 10;
+// 1 us for interval time range, changed accordingly
+int32_t tsMinIntervalTime = 1;
 
 // 20sec, the maximum value of stream computing delay, changed accordingly
 int32_t tsMaxStreamComputDelay = 20000;
diff --git a/src/os/src/detail/osTime.c b/src/os/src/detail/osTime.c
index 4d64e14d94..847d484d9e 100644
--- a/src/os/src/detail/osTime.c
+++ b/src/os/src/detail/osTime.c
@@ -348,6 +348,7 @@ int64_t convertTimePrecision(int64_t time, int32_t fromPrecision, int32_t toPrec
                                   {1.0 / 1000000, 1.0 / 1000,       1.} };
   return (int64_t)((double)time * factors[fromPrecision][toPrecision]);
 }
+
 static int32_t getDuration(int64_t val, char unit, int64_t* result, int32_t timePrecision) {
 
   switch (unit) {
diff --git a/src/tsdb/src/tsdbRead.c b/src/tsdb/src/tsdbRead.c
index b1c8633c02..2c44df0237 100644
--- a/src/tsdb/src/tsdbRead.c
+++ b/src/tsdb/src/tsdbRead.c
@@ -39,6 +39,12 @@ enum {
   TSDB_QUERY_TYPE_LAST     = 2,
 };
 
+enum {
+  TSDB_CACHED_TYPE_NONE    = 0,
+  TSDB_CACHED_TYPE_LASTROW = 1,
+  TSDB_CACHED_TYPE_LAST    = 2,
+};
+
 typedef struct SQueryFilePos {
   int32_t fid;
   int32_t slot;
@@ -2751,10 +2757,11 @@ bool tsdbNextDataBlock(TsdbQueryHandleT pHandle) {
   int64_t stime = taosGetTimestampUs();
   int64_t elapsedTime = stime;
 
+  // TODO refactor: remove "type"
   if (pQueryHandle->type == TSDB_QUERY_TYPE_LAST) {
-    if (pQueryHandle->cachelastrow == 1) {
+    if (pQueryHandle->cachelastrow == TSDB_CACHED_TYPE_LASTROW) {
       return loadCachedLastRow(pQueryHandle);
-    } else if (pQueryHandle->cachelastrow == 2) {
+    } else if (pQueryHandle->cachelastrow == TSDB_CACHED_TYPE_LAST) {
       return loadCachedLast(pQueryHandle);
     }
   }
@@ -2960,7 +2967,7 @@ out:
 }
 
 bool isTsdbCacheLastRow(TsdbQueryHandleT* pQueryHandle) {
-  return ((STsdbQueryHandle *)pQueryHandle)->cachelastrow > 0;
+  return ((STsdbQueryHandle *)pQueryHandle)->cachelastrow > TSDB_CACHED_TYPE_NONE;
 }
 
 int32_t checkForCachedLastRow(STsdbQueryHandle* pQueryHandle, STableGroupInfo *groupList) {
@@ -2978,9 +2985,9 @@ int32_t checkForCachedLastRow(STsdbQueryHandle* pQueryHandle, STableGroupInfo *g
   if (((STable*)pInfo->pTable)->lastRow) {
     code = tsdbGetCachedLastRow(pInfo->pTable, NULL, &key);
     if (code != TSDB_CODE_SUCCESS) {
-      pQueryHandle->cachelastrow = 0;
+      pQueryHandle->cachelastrow = TSDB_CACHED_TYPE_NONE;
     } else {
-      pQueryHandle->cachelastrow = 1;
+      pQueryHandle->cachelastrow = TSDB_CACHED_TYPE_LASTROW;
     }
   }
 
@@ -3000,12 +3007,11 @@ int32_t checkForCachedLast(STsdbQueryHandle* pQueryHandle) {
   int32_t code = 0;
   
   if (pQueryHandle->pTsdb && atomic_load_8(&pQueryHandle->pTsdb->hasCachedLastColumn)){
-    pQueryHandle->cachelastrow = 2;
+    pQueryHandle->cachelastrow = TSDB_CACHED_TYPE_LAST;
   }
 
   // update the tsdb query time range
   if (pQueryHandle->cachelastrow) {
-    pQueryHandle->window      = TSWINDOW_INITIALIZER;
     pQueryHandle->checkFiles  = false;
     pQueryHandle->activeIndex = -1;  // start from -1
   }
diff --git a/tests/script/general/parser/fill_us.sim b/tests/script/general/parser/fill_us.sim
index 8cd2c33347..762413d0a1 100644
--- a/tests/script/general/parser/fill_us.sim
+++ b/tests/script/general/parser/fill_us.sim
@@ -959,14 +959,14 @@ endi
 if $data31 != 9.000000000 then
   return -1
 endi
-if $data41 != null then
+if $data41 != NULL then
   print ===== $data41
   return -1
 endi
 if $data51 != 16.000000000 then
   return -1
 endi
-if $data61 != null then
+if $data61 != NULL then
    print ===== $data61
   return -1
 endi
diff --git a/tests/script/general/parser/last_cache.sim b/tests/script/general/parser/last_cache.sim
index 4b3285871b..9c414263ec 100644
--- a/tests/script/general/parser/last_cache.sim
+++ b/tests/script/general/parser/last_cache.sim
@@ -1,6 +1,6 @@
 system sh/stop_dnodes.sh
 system sh/deploy.sh -n dnode1 -i 1
-system sh/cfg.sh -n dnode1 -c walLevel -v 0
+system sh/cfg.sh -n dnode1 -c walLevel -v 1
 system sh/cfg.sh -n dnode1 -c maxtablesPerVnode -v 4
 system sh/exec.sh -n dnode1 -s start
 
diff --git a/tests/script/general/parser/testSuite.sim b/tests/script/general/parser/testSuite.sim
index 5f71138966..d7f06769a8 100644
--- a/tests/script/general/parser/testSuite.sim
+++ b/tests/script/general/parser/testSuite.sim
@@ -12,7 +12,7 @@ run general/parser/create_tb.sim
 run general/parser/dbtbnameValidate.sim
 run general/parser/fill.sim
 run general/parser/fill_stb.sim
-#run general/parser/fill_us.sim               #
+run general/parser/fill_us.sim
 run general/parser/first_last.sim
 run general/parser/import_commit1.sim
 run general/parser/import_commit2.sim