mysql模拟rank, dense_rank

参考http://stackoverflow.com/questions/532878/how-to-perform-grouped-ranking-in-mysql

CREATE TABLE `test` (
  `student_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `subject` varchar(10) CHARACTER SET latin1 DEFAULT NULL,
  `score` tinyint(4) DEFAULT NULL,
  PRIMARY KEY (`student_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (1,1,'yw',80);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (2,1,'sx',90);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (3,2,'yw',85);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (4,2,'sx',95);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (5,3,'yw',70);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (6,3,'sx',100);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (7,4,'yw',70);
insert  into `test`(`id`,`student_id`,`subject_name`,`score`) values (8,4,'sx',70);

subject_name: 科目 yw:语文 sx:数学
dense_rank

select subject_name as sbn , student_id as sid, score, 
@rank:=case when @sn <> subject_name then 1 when @score <> score then @rank+1 else @rank+0 end as rank, 
@sn := subject_name as sn, 
@score := score as score 
from `test` p, 
(select @rank := 0) r, 
(select @sn := '') u, 
(select @score := -1) i 
order by subject_name, score;

result:

sbn	sid	score	rank	sn	score
sx	4	70	1	sx	70
sx	1	90	2	sx	90
sx	2	95	3	sx	95
sx	3	100	4	sx	100
yw	3	70	1	yw	70
yw	4	70	1	yw	70
yw	1	80	2	yw	80
yw	2	85	3	yw	85

rank

select subject_name as sbn, student_id as sid, score, 
@rank:=case when @sn <> subject_name then 1 when @score <> score then @rank+@range else @rank+0 end as rank, 
@range:=case when @sn <> subject_name then 1 when @score = score then @range+1 else 1 end as ran , 
@sn := subject_name as sn, @score := score as sc
from `test` p, (select @rank := 0) r, 
(select @sn := '') u, (select @score := -1) i, (select @range := 1) g 
order by subject_name, score;

sbn	sid	score	rank	ran	sn	sc
sx	4	70	1	1	sx	70
sx	1	90	2	1	sx	90
sx	2	95	3	1	sx	95
sx	3	100	4	1	sx	100
yw	3	70	1	1	yw	70
yw	4	70	1	2	yw	70
yw	1	80	3	1	yw	80
yw	2	85	4	1	yw	85