public void next() {
      if (isMeasurementsExistPlaceholder) {
        if (!isDeviceExistPlaceholder && intoItems.size() > 1) {
          deviceIndex++;
        }
      } else {
        measurementIndex++;
        if (measurementIndex == intoItems.get(deviceIndex).getIntoMeasurements().size()) {
          deviceIndex++;
          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