数据库基本脚本

CREATE TABLE `a` (

`ID` INT(10) NULL DEFAULT NULL,

`class` INT(10) NULL DEFAULT NULL,

`score` INT(10) NULL DEFAULT NULL

)

COLLATE='utf8_general_ci'

ENGINE=InnoDB;

insert into a values (1,1,110);

insert into a values (2,1,120);

insert into a values (3,1,130);

insert into a values (4,1,140);

insert into a values (5,2,210);

insert into a values (6,2,220);

insert into a values (7,2,230);

insert into a values (8,2,240);

insert into a values (9,3,310);

insert into a values (10,3,320);

insert into a values (11,4,410);

1.　对 class进行分组 取每组的前2条

select id,class,score,rank from (

select b.id,b.class,b.score,@rownum:=@rownum+1 ,

if(@pdept=b.class,@rank:=@rank+1,@rank:=1) as rank,

@pdept:=b.class

from (

select id,class,score from a order by id

) b ,(select @rownum :=0 , @pdept := null ,@rank:=0) c ) result

having rank <3 ;

rank <3 指的相当月ruwnum<3 每组都自动给上了序号.多少条记录就多少个序号.指的是每组的.

2.  对 class 进行分组   取记录满足两天的,也就是rownum=2 的数据

select id,class,score,rank from (

select b.id,b.class,b.score,@rownum:=@rownum+1 ,

if(@pdept=b.class,@rank:=@rank+1,@rank:=1) as rank,

@pdept:=b.class

from (

select id,class,score from a order by score desc

) b ,(select @rownum :=0 , @pdept := null ,@rank:=0) c ) result

having rank =2 ;