public List<List<String>> getInputColumnNamesList() {
    if (step.isInputRaw()) {
      List<String> inputColumnNames =
          SqlConstant.COUNT_IF.equalsIgnoreCase(aggregationFuncName)
              ? Collections.singletonList(inputExpressions.get(0).getExpressionString())
              : inputExpressions.stream()
                  .map(Expression::getExpressionString)
                  .collect(Collectors.toList());
      return Collections.singletonList(inputColumnNames);
    }

    return Collections.singletonList(getInputColumnNames());
  }
Input of aggregation function. Currently, we only support one series in the aggregation
function.

<p>example: select sum(s1) from root.sg.d1; expression [root.sg.d1.s1] will be in this field.

<p>example: select sum(s1) from root.** group by level = 1; expression [root.sg.*.s1] may be in
this field if the data is in different DataRegion
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/parameter/AggregationDescriptor.java