code: @SuppressWarnings("unchecked")
      public <T> List<T> executeGroup(final Collection<ShardingExecuteGroup<? extends StatementExecuteUnit>> sqlExecuteGroups,
                                      final SQLExecuteCallback<T> firstCallback, final SQLExecuteCallback<T> callback) throws SQLException {
          try {
              return executeEngine.groupExecute((Collection) sqlExecuteGroups, firstCallback, callback, serial);
          } catch (final SQLException ex) {
              ExecutorExceptionHandler.handleException(ex);
              return Collections.emptyList();
          }
      }
docs: Execute group.
  
  @param sqlExecuteGroups SQL execute groups
  @param firstCallback first SQL execute callback
  @param callback SQL execute callback
  @param <T> class type of return value
  @return execute result
  @throws SQLException SQL exception