private void processTargetPathToSourceMap(
      Map<PartialPath, Map<String, String>> targetPathToSourceMap,
      Map<PartialPath, Map<String, InputLocation>> targetPathToSourceInputLocationMap,
      Map<String, InputLocation> sourceColumnToInputLocationMap) {
    for (Map.Entry<PartialPath, Map<String, String>> entry : targetPathToSourceMap.entrySet()) {
      PartialPath targetDevice = entry.getKey();
      Map<String, InputLocation> measurementToInputLocationMap = new HashMap<>();
      for (Map.Entry<String, String> measurementEntry : entry.getValue().entrySet()) {
        String targetMeasurement = measurementEntry.getKey();
        String sourceColumn = measurementEntry.getValue();
        measurementToInputLocationMap.put(
            targetMeasurement, sourceColumnToInputLocationMap.get(sourceColumn));
      }
      targetPathToSourceInputLocationMap.put(targetDevice, measurementToInputLocationMap);
    }
  }
This Visitor is responsible for transferring PlanNode Tree to Operator Tree.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/OperatorTreeGenerator.java