public Column[] filterBlock(Column[] columns) {
    if (isSelectAll()) {
      return columns;
    }
    if (isSelectNone()) {
      return Arrays.stream(columns).map(column -> column.getRegion(0, 0)).toArray(Column[]::new);
    }
    return getPositions(
        columns, Arrays.copyOf(selectedPositions, selectedPositionCount), 0, selectedPositionCount);
  }
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