private Column[] getPositions(
      Column[] originalColumns, int[] retainedPositions, int offset, int length) {
    requireNonNull(retainedPositions, "retainedPositions is null");

    Column[] columns = new Column[originalColumns.length];
    for (int i = 0; i < originalColumns.length; i++) {
      columns[i] = originalColumns[i].getPositions(retainedPositions, offset, length);
    }
    return columns;
  }
Creates a mask with the given selected positions. Selected positions must be sorted in
ascending order.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/relational/aggregation/AggregationMask.java