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