code: public List<AggregationDistinctSelectItem> getAggregationDistinctSelectItems() {
          List<AggregationDistinctSelectItem> result = new LinkedList<>();
          for (SelectItem each : items) {
              if (each instanceof AggregationDistinctSelectItem) {
                  result.add((AggregationDistinctSelectItem) each);
              }
          }
          return result;
      }
docs: Get aggregation distinct select items.
  
  @return aggregation distinct select items