数据库学习之旅——实验2

Posted 2022-12-12 Henry Zheng

本次实验的目的是对SQL语句中比较基础的部分，SELECT语句中的group by，order by，having，以及集合运算，聚集函数的学习与练习

由于无法上传附件SCHOOL数据库的信息，所以，这里只提交了数据库的表头，以及练习部分：

/*STUDENTS(SID,SNAME,EMAIL,GRADE);
TEACHERS(TID,TNAME,EMAIL,SALARY);
COURSES(CID,CNAME,HOUR);
CHOICES(NO,SID,TID,CID,SCORE);*/

--(1)查询年级为2001的所有学生的名称，按编号升序排列。
SELECT SNAME '学生名称'
FROM STUDENTS
WHERE GRADE='2001'
ORDER BY SID; 


--(2)查询学生的选课成绩合格的课程成绩，并把成绩换算为积点（60分对应积点为1，每增加1分，积点增加0.1）
SELECT SID '学生编号' , SCORE '学生成绩', (SCORE-50)/10 '积点'
FROM CHOICES
WHERE SCORE>'60';


--(3)查询课时是48或64的课程的名称
SELECT CNAME '课程名称'
FROM COURSES
WHERE HOUR IN('48','64');


--(4)查询所有课程名称中含有DATA的课程编号
SELECT CID '课程编号'
FROM COURSES
WHERE CNAME LIKE '%DATA%';


--(5)查询所有选课记录的课程号（不重复显示）
SELECT DISTINCT CID '课程号'
FROM CHOICES;


--(6)统计所有老师的平均工资
SELECT AVG(SALARY) '平均工资'
FROM TEACHERS;


--*********************************(7)查询所有学生的编号，姓名和平均成绩，按总平均成绩降序排列
SELECT STUDENTS.SID '学生编号' , SNAME '学生姓名' , AVG(SCORE) '平均成绩'
FROM CHOICES,STUDENTS
WHERE STUDENTS.SID=CHOICES.SID
GROUP BY STUDENTS.SID,STUDENTS.SNAME
ORDER BY AVG(SCORE)DESC;


--(8)统计各个课程的选课人数和平均成绩
SELECT CID '课程编号' , COUNT(NO)'选课人数' , AVG(SCORE)'平均成绩'
FROM CHOICES
GROUP BY CID;
--ORDER BY CID


--(9)查询至少选修了三门课程的学生的编号
SELECT SID '编号'
FROM CHOICES
GROUP BY SID
HAVING COUNT(*)>3


--(10)查询编号800009026的学生所选的全部课程的课程名和成绩
SELECT COURSES.CNAME,CHOICES.SCORE
FROM CHOICES,COURSES
WHERE CHOICES.SID='800009026' AND COURSES.CID=CHOICES.CID;


--(11)查询所有选了database的学生的编号
SELECT CHOICES.SID '学生编号'
FROM CHOICES,COURSES
WHERE COURSES.CNAME='database' AND CHOICES.CID=CHOICES.CID


--(12)求出选择了同一个课程的学生对
SELECT X.SID '学生1', Y.SID'学生2'
FROM CHOICES X,CHOICES Y
WHERE X.CID=Y.CID AND X.NO<Y.NO


--(13)求出至少被两名学生选修的课程编号
SELECT CHOICES.CID
FROM CHOICES
GROUP BY CHOICES.SID,CHOICES.CID 
HAVING COUNT(SID)>2


--(14)查询选修了编号850955252的学生所选的某个课程的学生编号
SELECT Y.SID
FROM CHOICES AS X, CHOICES AS Y
WHERE X.CID=Y.CID AND X.SID='850955252'


--(15)查询学生的基本信息及选修课程编号和成绩
SELECT STUDENTS.SID,SNAME,STUDENTS.EMAIL,GRADE,CHOICES.CID,SCORE
FROM STUDENTS,CHOICES
WHERE STUDENTS.SID=CHOICES.SID


--(16)查询学号850955252的学生的姓名和选修的课程名称及成绩
SELECT STUDENTS.SNAME,COURSES.CNAME,CHOICES.SCORE
FROM STUDENTS,COURSES,CHOICES
WHERE STUDENTS.SID=CHOICES.SID AND COURSES.CID=CHOICES.CID AND STUDENTS.SID='850955252'


--(17)查询学号850955252的学生同年级的所有学生资料
SELECT *
FROM STUDENTS
WHERE GRADE IN(
	SELECT STUDENTS.GRADE
	FROM STUDENTS
	WHERE STUDENTS.SID='850955252'
)


--(18)查询所有的有选课的学生的详细信息
SELECT *
FROM STUDENTS
WHERE SID IN(
	SELECT SID
	FROM CHOICES
)
/*
SELECT *
FROM STUDENTS
WHERE SID IN(
	SELECT CHOICES.SID
	FROM CHOICES,STUDENTS
	WHERE STUDENTS.SID=CHOICES.SID
)
*/


--(19)查询没有学生选的课程的编号
SELECT CID
FROM CHOICES
WHERE SID NOT IN(
	SELECT SID
	FROM CHOICES
)
/*
SELECT CID
FROM CHOICES
WHERE CID NOT IN(
	SELECT CID
	FROM CHOICES
)这两个一样吗？
*/



--(20)查询选修了课程名为C++的学生学号和姓名
SELECT STUDENTS.SID,STUDENTS.SNAME,COURSES.CNAME
FROM STUDENTS,COURSES,CHOICES
WHERE CHOICES.CID=COURSES.CID AND COURSES.CNAME='C++'
/*
SELECT SID,SNAME
FROM STUDENTS
WHERE SID IN(
	SELECT SID
	FROM CHOICES
	WHERE CID IN(
		SELECT CID
		FROM COURSES
		WHERE CNAME='C++'
	)	
)
问题：1.查询结果是否相同？ 2.如果结果相同，查询时间为什么不同？*/


--**********************************(21)找出选修课程成绩最差的选课记录
SELECT *
FROM CHOICES
WHERE CHOICES.SCORE >= ALL(
	SELECT SCORE
	FROM CHOICES
	WHERE SCORE IS NOT NULL
)


--(22)找出和课程UML或课程C++的课时一样的课程名称
SELECT CNAME
FROM COURSES
WHERE HOUR IN(
	SELECT HOUR
	FROM COURSES
	WHERE CNAME='UML' OR CNAME='C++'
)
/*
SELECT CNAME
FROM COURSES
WHERE HOUR =SOME(
	SELECT HOUR
	FROM COURSES
	WHERE CNAME='UML' OR CNAME='C++'
)
问题：IN 和 =SOME 的区别在哪里？*/


--(23)查询所有选修编号10001的课程的学生的姓名
SELECT DISTINCT SNAME
FROM STUDENTS,CHOICES
WHERE STUDENTS.SID=CHOICES.SID AND CID='10001'
/*
SELECT SNAME
FROM STUDENTS
WHERE EXISTS(
	SELECT *
	FROM CHOICES X
	WHERE X.CID='10001' AND X.SID=STUDENTS.SID
)
问题：区别在哪里？*/


--**********************************(24)查询选修了所有课程的学生姓名
SELECT SNAME
FROM STUDENTS
WHERE NOT EXISTS(
	SELECT *
	FROM COURSES AS X
	WHERE NOT EXISTS(
		SELECT *
		FROM CHOICES AS Y
		WHERE Y.SID=STUDENTS.SID AND Y.CID=X.CID
	)
)


--(25)利用集合运算，查询选修课程C++或课程Java的学生的编号
SELECT CHOICES.SID
FROM CHOICES,COURSES
WHERE (COURSES.CNAME='C++' OR COURSES.CNAME='JAVA') AND CHOICES.CID=COURSES.CID


--(26)实现集合交运算，查询既选修课程C++又选修课程Java的学生的编号
SELECT CHOICES.SID
FROM CHOICES,COURSES
WHERE (COURSES.CNAME='C++' AND COURSES.CNAME='JAVA') AND CHOICES.CID=COURSES.CID


--(27)实现集合减运算，查询选修课程C++而没有选修课程Java的学生的编号
SELECT CHOICES.SID
FROM CHOICES,COURSES
WHERE (COURSES.CNAME='C++' AND COURSES.CNAME<>'JAVA') AND CHOICES.CID=COURSES.CID