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

/*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

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

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

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

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

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

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

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

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

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

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

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

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

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

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






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