refactor(query): constant NULL value processing logic

TD-14802
TD-14803

source/common/src/tdatablock.c

@@ -1100,6 +1100,11 @@ int32_t colInfoDataEnsureCapacity(SColumnInfoData* pColumn, uint32_t numOfRows)
 
     pColumn->nullbitmap = tmp;
     memset(pColumn->nullbitmap, 0, BitmapLen(numOfRows));
+
+    if (pColumn->info.type == TSDB_DATA_TYPE_NULL) {
+      return TSDB_CODE_SUCCESS;
+    }
+
     assert(pColumn->info.bytes);
     tmp = taosMemoryRealloc(pColumn->pData, numOfRows * pColumn->info.bytes);
     if (tmp == NULL) {

source/libs/scalar/src/scalar.c

@@ -440,8 +440,10 @@ EDealRes sclRewriteFunction(SNode** pNode, SScalarCtx *ctx) {
     return DEAL_RES_ERROR;
   }
 
+  if (colDataIsNull_s(output.columnData, 0)) {
+    res->node.resType.type = TSDB_DATA_TYPE_NULL;
+  } else {
     res->node.resType = node->node.resType;
-
     int32_t type = output.columnData->info.type;
     if (IS_VAR_DATA_TYPE(type)) {
       res->datum.p = output.columnData->pData;
@@ -449,6 +451,7 @@ EDealRes sclRewriteFunction(SNode** pNode, SScalarCtx *ctx) {
     } else {
       memcpy(nodesGetValueFromNode(res), output.columnData->pData, tDataTypes[type].bytes);
     }
+  }
 
   nodesDestroyNode(*pNode);
   *pNode = (SNode*)res;