题解 | #每类试卷得分前3名#

1、ROW_NUMBER()OVER(PARTITION BY XX ORDER BY XX) DESC,XX DESC,XX DESC)按优先级排序
2、注意 left join嵌套组合的表记得重新命名，不然取不到数
3、这里要以 exam_record的数据为基础，不能直接用join函数，需要用到left join或right join
4、 嵌套的表里面记得按tag,uid做好分组显示

select tag,uid, ranking
from (
select tag, uid, 
ROW_NUMBER()OVER(PARTITION BY tag ORDER BY max(score) DESC,min(score) DESC,uid DESC) ranking
 FROM examination_info b 
right JOIN exam_record  a
using(exam_id)
GROUP BY tag,uid) c

where ranking <=3