Merge pull request #15500 from taosdata/fix/TS-1719-V26

first last and count combine aggregate is slower 

src/query/src/qExecutor.c

@@ -2814,6 +2814,7 @@ static bool notContainSessionOrStateWindow(SQueryAttr *pQueryAttr) { return !(pQ
 static int32_t updateBlockLoadStatus(SQueryAttr *pQuery, int32_t status) {
   bool hasFirstLastFunc = false;
   bool hasOtherFunc = false;
+  bool hasCount = false;
 
   if (status == BLK_DATA_ALL_NEEDED || status == BLK_DATA_DISCARD) {
     return status;
@@ -2829,6 +2830,8 @@ static int32_t updateBlockLoadStatus(SQueryAttr *pQuery, int32_t status) {
 
     if (functionId == TSDB_FUNC_FIRST_DST || functionId == TSDB_FUNC_LAST_DST) {
       hasFirstLastFunc = true;
+    } else if(functionId == TSDB_FUNC_COUNT) {
+      hasCount = true;  
     } else {
       hasOtherFunc = true;
     }
@@ -2836,7 +2839,7 @@ static int32_t updateBlockLoadStatus(SQueryAttr *pQuery, int32_t status) {
 
   if (hasFirstLastFunc && status == BLK_DATA_NO_NEEDED) {
     if(!hasOtherFunc) {
-      return BLK_DATA_DISCARD;
+      return hasCount ? BLK_DATA_NO_NEEDED : BLK_DATA_DISCARD;
     } else {
       return BLK_DATA_ALL_NEEDED;
     }