Oracle

(SELECT v_weekly_content
          FROM (SELECT ROW_NUMBER () OVER (PARTITION BY n_group_seq ORDER BY d_weekly_date DESC)
                                                                           rm,
                       n_group_seq, v_weekly_content
                  FROM tbl_document_projectweekly pw)
         WHERE rm = 1 AND n_group_seq = g.n_group_seq) projectweekly

 PARTITION BY 代表分区字段

 OVER在分区的基础上

  ROW_NUMBER () 根据排序给分区的记录增加序号