oracle group by用法

分组第一个：

SELECT * FROM (SELECT ROW_NUMBER() OVER(PARTITION BY dlr_id ORDER BY user_id DESC) rn,
　　u.user_id,u.dlr_id FROM tm_user u where dlr_id='1000001812')
　　WHERE rn = 1  ;




select user_id,dlr_id from tm_user tu where tu.rowid in (
select max(rowid) from(
select user_id,dlr_id from tm_user)
group by dlr_id) and dlr_id='1000001812';

Oracle分组排名

情境：只查询某个条件下的N条件记录，如每个分类下查询（前）5条


例：(相同商户号只查5条)
[sql] view plaincopy


    select *  
      from (select t.mer_code,  
                   t.li_goods_name,  
                   t.li_id,  
                   dense_rank() over(partition by t.mer_code order by t.li_id) rk  
              from yd_mer_listing t)  
     where rk < 6  




说明：rank()的排名是按over()内order by决定的，如果order by的字段值是一样的，那么rank()排名也一样。


优势：如果用in语句，如 … where t.li_id in (select LI_ID from yd_mer_listing m where rownum < 6 and m.mer_code = t.mer_code and m.LI_STATE = '3' )…效率会很低