@Override
  protected String getExpressionStringInternal() {
    return "group by time(["
        + startTime
        + ", "
        + endTime
        + "], "
        + interval
        + ", "
        + slidingStep
        + ")";
  }
Only used for representing GROUP BY TIME filter.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/other/GroupByTimeExpression.java