50个SQL语句(MySQL版) 问题二十二

--------------------------表结构--------------------------

student(StuId,StuName,StuAge,StuSex) 学生表

teacher(TId,Tname) 教师表

course(CId,Cname,C_TId) 课程表

sc(SId,S_CId,Score) 成绩表

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问题二十二：查询如下课程成绩第3名到第6名的学生成绩单：企业管理（001），马克思（002），UML（003），数据库（004）格式：[学生ID]，[学生姓名]，企业管理，马克思，UML，数据库，平均成绩

SELECT stu.StuId,stu.StuName,
BM.Score AS BM,Marx.Score AS Marx,UML.Score AS UML,DB.Score AS DB,
(IFNULL(BM.Score,0)+IFNULL(Marx.Score,0)+IFNULL(UML.Score,0)+IFNULL(DB.Score,0))/
(SUM(CASE WHEN IFNULL(BM.Score,0)=0 THEN 0 ELSE 1 END)+
SUM(CASE WHEN IFNULL(Marx.Score,0)=0 THEN 0 ELSE 1 END)+
SUM(CASE WHEN IFNULL(UML.Score,0)=0 THEN 0 ELSE 1 END)+
SUM(CASE WHEN IFNULL(DB.Score,0)=0 THEN 0 ELSE 1 END)) AS AvgScore
FROM student stu
LEFT JOIN sc AS BM ON BM.SId=stu.StuId AND BM.S_CId='001'
LEFT JOIN sc AS Marx ON Marx.SId=stu.StuId AND Marx.S_CId='002'
LEFT JOIN sc AS UML ON UML.SId=stu.StuId AND UML.S_CId='003'
LEFT JOIN sc AS DB ON DB.SId=stu.StuId AND DB.S_CId='004'
GROUP BY stu.StuId
ORDER BY AvgScore DESC
LIMIT 2,4;

答案仅供参考，不一定完全正确，若发现错误或有更好的，欢迎评论，互相交流，一起成长！！！