code: @SuppressWarnings("unchecked")
      protected K createKey(QueryParameters params) throws MjdbcException {
          K result = null;
  
          if (columnName == null) {
              result = (K) params.getValue(params.getNameByPosition(columnIndex));
          } else {
              result = (K) params.getValue(columnName);
          }
  
          return result;
      }
docs: Generates key for query output row
  
  @param params query output row
  @return key for query output row
  @throws org.midao.jdbc.core.exception.MjdbcException