MYSQL 分组排名

今天遇到一个MYSQL排序的问题,要求按某列进行分组,组内进行排序.

百度一下发现MYSQL不支持row_number(),rank()等函数.

采用的办法如下,我们首先创建一个测试表:

--创建表
create table Rank_test(ID int,SCORE int,grp int)

--插入数据
insert into Rank_test values(1 ,     28,1);
insert into Rank_test values(2 ,     33,1);
insert into Rank_test values(3 ,     33,1);
insert into Rank_test values(4 ,     89,1);
insert into Rank_test values(5 ,     99,1);
insert into Rank_test values(6 ,     68,1);
insert into Rank_test values(7 ,     68,1);
insert into Rank_test values(8 ,     78,1);
insert into Rank_test values(9 ,     88,1);
insert into Rank_test values(10,    90 ,1);
insert into Rank_test values(11,     28,2);
insert into Rank_test values(12,     33,2);
insert into Rank_test values(13,     33,2);
insert into Rank_test values(14,     89,2);
insert into Rank_test values(15,     99,2);
insert into Rank_test values(16,     68,2);
insert into Rank_test values(17,     68,2);
insert into Rank_test values(18,     78,2);
insert into Rank_test values(19,     88,2);
insert into Rank_test values(20,    90 ,2);         

分组排序的SQL代码:

SELECT id,
       score,
       rank
  FROM (SELECT tmp.id,
               tmp.score,
               @rank := (case when @Grp = grp then @rank + 1 else 1 end) AS rank  ,
               @Grp:=grp as grp2
          FROM (SELECT id,
                       score,
                       grp
                  FROM rank_test) tmp,
               (SELECT @rank   := 0,@grp:=0) a
            order by grp,score desc) RESULT
;  

结果如下:

测试结果OK,但重点是套用到我们的SQL中后,排序结果完全不是我们预期中的,而且没有找到规律.

经过几次尝试,最后重新改写了SQL代码,终于成功了.

原因是套用下面这段代码时,我们是用了几张表进行关联(inner join ),最后将inner join 的表全部改为where 语句中的子句,结果满足我们的预期.

(SELECT id,
                       score,
                       grp
                  FROM rank_test) tmp,

所以建议在这里的代码尽量使用单表,不要多张表关联

附上修改前后的代码:(红色部分是修改前,绿色部分是修改后)

select * from (
select evtdate
        ,stkabb,chng,PCTCSHG,cshg,SHHNAME
        ,@rank := (case when @SHHNAME=SHHNAME then @rank + 1
                                        else 1 end) AS rank
        ,@SHHNAME:=SHHNAME
from
(
select tt.SHHNAME -- 股东名称
      ,s.evtdate  -- 变动日期
      ,r.stkabb   -- 变动股票名称
      ,ifnull(s.RLDSHG,s.cshg-s.SHGBCH)/10000 as chng -- 变动股数（万股）
      ,s.cshg/10000 as cshg-- 变动后持股（万股）
      ,s.PCTCSHG -- 变动后持股比例%
  from pgenius.hk_stkcode r
 inner join pgenius.HK_SAKCHMJSHH s
    on r.comunic = s.comunic
 inner join
      (select distinct b.SHHNAME
         from pgenius.hk_stkcode a
        inner join pgenius.HK_SAKCHMJSHH b
           on a.comunic = b.comunic
          and b.evtdate = (select max(evtdate) from pgenius.HK_SAKCHMJSHH
                            where comunic = b.comunic and SHHNAME = b.SHHNAME and NTUREFCINTRTS = b.NTUREFCINTRTS)
        where a.lssturefc = 1
          and b.cshg > 0
          and a.stkcode = ''
       ) tt
    on s.SHHNAME = tt.SHHNAME
) t1,
(SELECT @rank := 0,@SHHNAME:='') t2
order by SHHNAME,evtdate desc,stkabb ) t

select t.*
        , o.stkabb
from
(
    select t1.*
            ,@rank := (case when @SHHNAME=SHHNAME then @rank + 1
                                            else 1 end) AS rank
            ,@SHHNAME:=SHHNAME
    from
    (
        select s.evtdate
                    ,ifnull(s.RLDSHG,s.cshg-s.SHGBCH)/10000 as chng -- 变动股数（万股）
                    ,s.cshg/10000 as cshg-- 变动后持股（万股）
                    ,s.PCTCSHG -- 变动后持股比例%
                    ,SHHNAME
                    ,s.COMUNIC
        from pgenius.HK_SAKCHMJSHH s
        where SHHNAME in (
        select distinct shhname from pgenius.HK_SAKCHMJSHH a
        where comunic=(select COMUNIC from pgenius.hk_stkcode where stkcode='')
            and ISVALID=1
            and not exists(select 1 from pgenius.HK_SAKCHMJSHH where COMUNIC=a.COMUNIC and SHHNAME=a.SHHNAME and evtdate>a.evtdate)
            and cshg > 0)
    ) t1,
    (SELECT @rank := 0,@SHHNAME:='') t2
    order by SHHNAME,evtdate desc
) t
    inner join pgenius.hk_stkcode o on t.COMUNIC= o.COMUNIC
where t.rank<=10
order by shhname,rank