常見學生課表成績數據庫查詢

1. 在表中插入符合主鍵
[sql] 
/*成績表*/ 
CREATE TABLE SC  
(  
Sid INT REFERENCES Student(Sid), /*學生學號*/ 
Cid INT REFERENCES Course(Cid), /*課程編號*/ 
Score INT NOT NULL, /*課程分數*/ 
PRIMARY KEY(Sid,Cid) /*將學生學號和課程編號設爲複合主鍵*/ 
)  
 
2. 查詢各科成績最高分，最低分以及平均分
[sql] 
SELECT c.Cname, MAX(s.Score) AS Max, MIN(s.Score) AS Min, AVG(s.Score) AS Average   
FROM Course c JOIN SC s ON c.Cid = s.Cid   
GROUP BY c.Cname   
/*此處應注意，若不按照c.Cname進行分組，SQL語句會報錯，c.Cname在SELECT語句中不合法，因爲它  
並未出現在聚合函數中也沒有出現在GROUP BY語句中*/ 
 
 
3. 查詢平均成績大於80分的學生姓名以及平均成績
[sql] 
SELECT Sname, AVG(Score) AS Average FROM Student JOIN SC   
ON Student.Sid=SC.Sid   
GROUP BY Sname  
HAVING AVG(Score)>80   
/*以聚合函數爲條件進行刪選只能在HAVING語句中進行，WHERE語句不支持聚合函數*/ 
 
 
4. 查詢各學生都選了多少門課
[sql] 
SELECT Sname, COUNT(Cid) AS TOTAL_COURSE FROM Student   
LEFT JOIN SC ON Student.Sid=SC.Sid  
GROUP BY Sname  
/*使用LEFT JOIN可以將一門課也沒有選的學生也查詢出來，  
若不加LEFT查不出DAISY和SHERRY*/ 
 
 
5. 查詢沒有選JANE老師課的學生信息
[sql] 
SELECT s.Sid,s.Sname,s.Sage,s.Sage FROM Student s   
WHERE s.Sid NOT IN  
(SELECT s.Sid FROM SC s JOIN Course c ON s.Cid=c.Cid   
JOIN Teacher t ON c.Tid=t.Tid   
WHERE t.Tname='JANE')  
/*子查詢中查詢出所有選擇JANE老師課的學生學號，  
主查詢去查詢在學生表中但不在子查詢結果集中的學生信息*/ 
 
 
6. 查詢既選擇了COMPUTER課程，又選擇了MATH課程的學生信息
[sql] 
SELECT s.Sid,s.Sname,s.Sage,s.Ssex FROM STUDENT s   
JOIN SC ss ON s.Sid=ss.Sid  
JOIN Course c ON ss.Cid=c.Cid WHERE c.Cname='COMPUTER' 
INTERSECT 
SELECT s.Sid,s.Sname,s.Sage,s.Ssex FROM STUDENT s   
JOIN SC ss ON s.Sid=ss.Sid  
JOIN Course c ON ss.Cid=c.Cid WHERE c.Cname='MATH' 
/*第一個查詢查詢出選擇COMPUTER課程的學生信息，  
第二個查詢查詢出選擇MATH課程的學生信息，  
用INTERSECT關鍵字取交集*/ 
 
 
7. 查詢COMPUTER課程比MATH課程分數高的學生學號
[sql] 
SELECT a.Sid FROM  
(SELECT s.Sid,s.Score FROM SC s JOIN Course c ON s.Cid=c.Cid WHERE c.Cname='COMPUTER') a  
JOIN 
(SELECT s.Sid,s.Score FROM SC s JOIN Course c ON s.Cid=c.Cid WHERE c.Cname='MATH') b  
ON a.Sid=b.Sid  
WHERE a.Score>b.Score  
/*將選了COMPUTER課的學生學號和成績和選了MATH課的學生學號和成績連接  
WHERE語句限制COMPUTER課的成績高於MATH課*/ 
 
 
8. 查詢和JOHN選的課相同的學生信息
[sql] 
SELECT Student.Sname FROM Student JOIN SC ON Student.Sid=SC.Sid  
WHERE SC.Cid IN 
(SELECT SC.Cid FROM SC JOIN Student ON SC.Sid=Student.Sid WHERE Student.Sname='JOHN') /*查詢選了的課JOHN也都選了的學生的姓名*/ 
AND Student.Sname<>'JOHN' /*限制該學生不能是JOHN本人*/ 
GROUP BY Student.Sname   
HAVING COUNT(SC.Cid)=  
(SELECT COUNT(*) FROM SC JOIN Student ON SC.Sid=Student.Sid WHERE Student.Sname='JOHN') /*該學生選的課程總數與JOHN選的課程總數相同*/ 
 
 
9. 按總分爲學生排名，總分相同名次相同
[sql] 
SELECT RANK() OVER (ORDER BY SUM(ss.Score) DESC) AS Rank, s.Sname, ISNULL(SUM(ss.Score),0)   
FROM Student s LEFT JOIN SC ss   
ON s.Sid = ss.Sid   
GROUP BY s.Sname   
ORDER BY SUM(ss.Score) DESC 
/*RANK()是SQL Server的一個built-in函數，語法爲  
RANK() OVER ( [ partition_by_clause ] order_by_clause ).*/ 
 
 
10. 查詢總分在100至200之間的學生姓名及總分
[sql] 
SELECT s.Sname,SUM(ss.Score) FROM Student s JOIN SC ss ON s.Sid=ss.Sid  
GROUP BY s.Sname HAVING SUM(ss.Score) BETWEEN 100 AND 200  
 
 
11. 查詢總分第六到十名的學生姓名以及總分
[sql] 
SELECT * FROM 
(SELECT TOP(5) * FROM 
(SELECT TOP(10) SC.Sid,SUM(SC.Score) AS SUM FROM SC GROUP BY SC.Sid ORDER BY SUM(SC.Score)) a  
ORDER BY a.SUM) b  
ORDER BY b.SUM DESC 
/*SELECT TOP(10) SC.Sid,SUM(SC.Score) AS SUM FROM SC GROUP BY SC.Sid ORDER BY SUM(SC.Score)查詢出總分前十名  
SELECT TOP(5) FROM (...) a ORDER BY a.SUM查詢出成績六到十名  
SELECT * FROM (...) b ORDER BY b.SUM DESC將結果倒序按照從高分到低分排列*/ 
 
 
12. 查詢各科成績的前三名以及分數
[sql] 
SELECT s.Sid,s.Cid,s.Score FROM SC s   
WHERE s.Score IN  
(SELECT TOP(3) Score FROM SC WHERE s.Cid= Cid ORDER BY score DESC)   
ORDER BY s.Cid;  
/*從SC表中查詢出學生學號，課程編號以及成績，WHERE子句限制了查詢出的記錄成績必須在子查詢集合內  
子查詢查詢出了各科成績的前三名並通過課程編號和主查詢關聯*/  
 
 
13. 查詢有不及格科目的學生的姓名，不及格科目以及不及格科目成績
[sql] 
SELECT s.Sname,c.Cname,ss.Score FROM Student s JOIN SC ss ON s.Sid=ss.Sid JOIN Course c ON ss.Cid=c.Cid  
WHERE ss.Score<60  
 
 
14. 查詢所有學生都選修的課程
[sql] 
SELECT c.Cname FROM SC s JOIN Course c ON s.Cid=c.Cid   
GROUP BY c.Cname HAVING COUNT(s.Sid)=(SELECT COUNT(*) FROM Student)  
 
15. 查詢選修了兩門或以上的學生姓名及選修總科目
[sql] 
SELECT s.Sname,COUNT(ss.Cid) AS TOTAL FROM Student s JOIN SC ss ON s.Sid=ss.Sid   
GROUP BY s.Sname HAVING COUNT(ss.Cid)>1