code: public <T> List<T> executeGroup(final Collection<ShardingExecuteGroup<? extends StatementExecuteUnit>> sqlExecuteGroups, final SQLExecuteCallback<T> callback) throws SQLException {
          return executeGroup(sqlExecuteGroups, null, callback);
      }
docs: Execute group.
  
  @param sqlExecuteGroups SQL execute groups
  @param callback SQL execute callback
  @param <T> class type of return value
  @return execute result
  @throws SQLException SQL exception