mysql 查询前三的数据_MySQL 查询各科前三的数据

方法一：

SELECT sc.*,c.`

Cname` ,COUNT(sc.C)

FROM sc

LEFT JOIN sc a

ON sc.C = a.C AND sc.score >= a.score

LEFT JOIN course c

ON sc.C = c.C

WHERE sc.C = c.C

GROUP BY

sc.C,sc.S,sc.score

HAVING COUNT(sc.C)>=4

ORDER BY a.C,a.score DESC

解析：

先copy 一个sc 表中的数据，与原sc 进行对比。统计每个score 大于其他数据的计数。再按sc.C,sc.S进行分组

SELECT sc.*,COUNT(sc.C)

FROM sc

LEFT JOIN sc a

ON sc.C= a.C AND sc.score >=a.score

GROUP BY sc.C,sc.S

可以看到，第一行数据的count计数为 6，由于我们要取每科前三名，sc表中共有student S编号7个，

自身不纳入count进行计数，则为6个需要取出前3--计数大于3的值。

SELECT sc.*,COUNT(sc.C)

FROM sc

LEFT JOIN sc a

ON sc.C= a.C AND sc.score >=a.score

GROUP BY

sc.C,sc.S,sc.score

HAVING COUNT(sc.C)>3ORDER BY a.C,a.score DESC

方法二：

SELECT a.* FROM

sc a

WHERE

(SELECT COUNT(*)

FROM sc

WHERE sc.C =a.C

AND a.score

ORDER BY a.C,a.score DESC

解析：

与方法一同理，复制一个表进行count计数