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获取每类科目的前几条记录

今天有同事问一下sql语句的写法，以前见过是分两段做的，google了下，发现已经有人有简单的方案了。
本人已经测试过，是符合要求的。

文章的地址为： http://wenku.baidu.com/view/6830f0d850e2524de5187e35.html

代码如下

建表语句
create table test_qjk_score(
stu int primary key,
subject varchar2(30),
mark int
);

insert into test_qjk_score(stu,subject,mark)values(1,'语文',85);
insert into test_qjk_score(stu,subject,mark)values(2,'语文',15);
insert into test_qjk_score(stu,subject,mark)values(3,'语文',25);
insert into test_qjk_score(stu,subject,mark)values(4,'语文',35);
insert into test_qjk_score(stu,subject,mark)values(5,'语文',45);
insert into test_qjk_score(stu,subject,mark)values(6,'语文',55);
insert into test_qjk_score(stu,subject,mark)values(7,'语文',65);
insert into test_qjk_score(stu,subject,mark)values(8,'语文',75);

insert into test_qjk_score(stu,subject,mark)values(9,'数学',83);
insert into test_qjk_score(stu,subject,mark)values(10,'数学',13);
insert into test_qjk_score(stu,subject,mark)values(11,'数学',23);
insert into test_qjk_score(stu,subject,mark)values(12,'数学',33);
insert into test_qjk_score(stu,subject,mark)values(13,'数学',43);
insert into test_qjk_score(stu,subject,mark)values(14,'数学',53);
insert into test_qjk_score(stu,subject,mark)values(15,'数学',63);
insert into test_qjk_score(stu,subject,mark)values(16,'数学',73);


insert into test_qjk_score(stu,subject,mark)values(17,'英语',87);
insert into test_qjk_score(stu,subject,mark)values(18,'英语',17);
insert into test_qjk_score(stu,subject,mark)values(19,'英语',27);
insert into test_qjk_score(stu,subject,mark)values(20,'英语',37);
insert into test_qjk_score(stu,subject,mark)values(21,'英语',47);
insert into test_qjk_score(stu,subject,mark)values(22,'英语',57);
insert into test_qjk_score(stu,subject,mark)values(23,'英语',67);
insert into test_qjk_score(stu,subject,mark)values(24,'英语',77);

执行

select * from (select rank() over(partition by subject order by mark desc) rk,test_qjk_score.* from test_qjk_score) T  where T.rk<=3;

就可以得到结果了,结果如下:

RK    STU           SUBJECT    MARK
1        9             数学    83
2       16            数学    73
3       15            数学    63
1       17           英语    87
2       24           英语    77
3      23            英语    67
1      1             语文    85
2      8             语文    75
3      7             语文    65


------使用案例------
begin tran T1
select COUNT(*) from DeviceLocationTracks TA

delete from TA
from DeviceLocationTracks TA
left outer join (select RANK() over(partition by gpstime order by ID desc) rk, DeviceLocationTracks.* from DeviceLocationTracks) TB
on TA.ID = TB.ID
where TB.rk > 1

select COUNT(*) from DeviceLocationTracks TA

rollback tran T1