code: public int[] getBoundsInTileIndex( int zoomlevel ) throws Exception {
          String sql = "select min(tile_column), max(tile_column), min(tile_row), max(tile_row) from tiles where zoom_level="
                  + zoomlevel;
          return database.execOnConnection(connection -> {
              try (IHMStatement statement = connection.createStatement(); IHMResultSet resultSet = statement.executeQuery(sql);) {
                  if (resultSet.next()) {
                      int minTx = resultSet.getInt(1);
                      int maxTx = resultSet.getInt(2);
                      int minTy = resultSet.getInt(3);
                      int maxTy = resultSet.getInt(4);
                      return new int[]{minTx, maxTx, minTy, maxTy};
                  }
              }
              return null;
          });
      }
docs: Get the bounds of a zoomlevel in tile indexes.
  
  <p>This comes handy when one wants to navigate all tiles of a zoomlevel.
  
  @param zoomlevel the zoom level.
  @return the tile indexes as [minTx, maxTx, minTy, maxTy].
  @throws Exception