学生表/教师表/课程表/成绩表常见SQL查询

1. 在表中插入符合主键
[sql]
/*成绩表*/
CREATE TABLE SC
(
Sid INT REFERENCES Student(Sid), /*学生学号*/
Cid INT REFERENCES Course(Cid), /*课程编号*/
Score INT NOT NULL, /*课程分数*/
PRIMARY KEY(Sid,Cid) /*将学生学号和课程编号设为复合主键*/
)

2. 查询各科成绩最高分，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
/*此处应注意，若不按照c.Cname进行分组，SQL语句会报错，c.Cname在SELECT语句中不合法，因为它
并未出现在聚合函数中也没有出现在GROUP BY语句中*/

3. 查询平均成绩大于80分的学生姓名以及平均成绩
[sql]
SELECT Sname, AVG(Score) AS Average FROM Student JOIN SC
ON Student.Sid=SC.Sid
GROUP BY Sname
HAVING AVG(Score)>80
/*以聚合函数为条件进行删选只能在HAVING语句中进行，WHERE语句不支持聚合函数*/

4. 查询各学生都选了多少门课
[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可以将一门课也没有选的学生也查询出来，
若不加LEFT查不出DAISY和SHERRY*/

5. 查询没有选JANE老师课的学生信息
[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')
/*子查询中查询出所有选择JANE老师课的学生学号，
主查询去查询在学生表中但不在子查询结果集中的学生信息*/

6. 查询既选择了COMPUTER课程，又选择了MATH课程的学生信息
[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'
/*第一个查询查询出选择COMPUTER课程的学生信息，
第二个查询查询出选择MATH课程的学生信息，
用INTERSECT关键字取交集*/

7. 查询COMPUTER课程比MATH课程分数高的学生学号
[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
/*将选了COMPUTER课的学生学号和成绩和选了MATH课的学生学号和成绩连接
WHERE语句限制COMPUTER课的成绩高于MATH课*/

8. 查询和JOHN选的课相同的学生信息
[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') /*查询选了的课JOHN也都选了的学生的姓名*/
AND Student.Sname<>'JOHN' /*限制该学生不能是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') /*该学生选的课程总数与JOHN选的课程总数相同*/

9. 按总分为学生排名，总分相同名次相同
[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的一个built-in函数，语法为
RANK() OVER ( [ partition_by_clause ] order_by_clause ).*/

10. 查询总分在100至200之间的学生姓名及总分
[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. 查询总分第六到十名的学生姓名以及总分
[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)查询出总分前十名
SELECT TOP(5) FROM (...) a ORDER BY a.SUM查询出成绩六到十名
SELECT * FROM (...) b ORDER BY b.SUM DESC将结果倒序按照从高分到低分排列*/

12. 查询各科成绩的前三名以及分数
[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;
/*从SC表中查询出学生学号，课程编号以及成绩，WHERE子句限制了查询出的记录成绩必须在子查询集合内
子查询查询出了各科成绩的前三名并通过课程编号和主查询关联*/

13. 查询有不及格科目的学生的姓名，不及格科目以及不及格科目成绩
[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. 查询所有学生都选修的课程
[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. 查询选修了两门或以上的学生姓名及选修总科目
[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