code: public ColumnType[] columnTypes() {
          ColumnType[] columnTypes = new ColumnType[columnCount()];
          for (int i = 0; i < columnCount(); i++) {
              columnTypes[i] = columns().get(i).type();
          }
          return columnTypes;
      }
docs: Returns an array of the column types of all columns in the relation, including duplicates as appropriate,
  and maintaining order