MySQL排名 保留名次空缺 问题

Posted 2020-12-12 limalove

思路：主要是看每门课程下，对于每个分数，该课程大于该分数的有几个

 

 

 

保留名次空缺：

select a.cid, a.sid, a.score , count(a.score<b.score)+1 as rank
from sc a left join sc b on a.cid=b.cid and a.score<b.score   #笛卡尔积连接, 然后筛选满足a.score<b.score的
group by a.cid, a.sid
order by a.cid, a.score desc;

 

 

不保留名次空缺：

select a.cid, a.sid, a.score , count(distinct b.score)+1 as rank  #这里使用的是distinct b.score
from sc a left join sc b on a.cid=b.cid and a.score<b.score   #笛卡尔积连接, 然后筛选满足a.score<b.score的
group by a.cid, a.sid
order by a.cid, a.score desc;

 

 

 

中间表的形式：

select a.cid,a.sid,a.score,b.cid,b.sid,b.score
from  sc a left join sc b on a.cid=b.cid and a.score< b.score
order by a.cid, a.score desc;

 

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