public void nextMeasurement() {
      if (!intoItems.get(deviceIndex).isMeasurementsExistPlaceholder()) {
        measurementIndex++;
        if (measurementIndex == intoItems.get(deviceIndex).getIntoMeasurements().size()) {
          measurementIndex = 0;
        }
      }
    }
This class maintains information of {@code INTO} clause.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/statement/component/IntoComponent.java