sqlserver 多表連接查詢

已有三張表
student表：

選課表SC:

課程表Course:

1. 查詢每個學生的學號、姓名、課程代號及選課成績，不允許有重複列

SELECT Student.SID,Student.Sname,SC.CID,SC.Scores
FROM Student INNER JOIN SC ON Student.SID=SC.SID

2. 查詢每個學生的學號、姓名、課程名及選課成績

SELECT Student.SID,Student.Sname,Course.Cname,SC.Scores
FROM Student INNER JOIN SC ON Student.SID=SC.SID INNER JOIN Course ON SC.CID=Course.CID

3. 查詢哪些課程沒人選

SELECT Course.Cname
FROM Course LEFT OUTER JOIN SC ON course.cid = sc.cid
WHERE Scores IS NULL

4. 查詢男生中沒選課的學號、姓名、性別

SELECT Student.SID,Sname,Sex
FROM Student LEFT OUTER JOIN SC ON Student.SID=SC.SID
WHERE Sex=‘男’ AND Scores IS NULL

5.查詢每個男生的選課門數，包括沒有選課的男生，結果按照選課門數遞減排序。

SELECT Student.Sname,COUNT(SC.Scores) AS 選課門數
FROM Student LEFT OUTER JOIN SC ON Student.SID=SC.SID
WHERE Sex=‘男’
GROUP BY Sname
ORDER BY 選課門數 DESC