摘要： 表結構： student(s#,sname,sage,ssex)學生表 course（c#,cname,T#）課程表 sc(s#,c#,score)成績表 Teacher(T#,tname)教師表 1.查詢001課程比002課程成績高的所有學生的學號： select sc1.s# from sc sc1 join sc sc2 on sc1.s# = sc2.s

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表結構：

student(s#,sname,sage,ssex)學生表 
course（c#,cname,T#）課程表 
sc(s#,c#,score)成績表 
Teacher(T#,tname)教師表

1.查詢001課程比002課程成績高的所有學生的學號：

select sc1.s# 
from sc sc1 join sc sc2 on sc1.s# = sc2.s# 
where sc1.c# = ‘001’ and sc2.c# = ‘002’ and sc1.score > sc2.score

2.查詢平均成績大於60分的同學的學號和平均成績：

select s#, avg
 
(score) from sc group by s# having avg(score)>60;

3.查詢所有同學的學號，姓名，選課數，總成績：

select student.s#,student.name ,count(sc.c#) ,sum(sc.score) 
from student left join sc on student.s# = sc.s# 

注：內連線要計算笛卡爾積，這裡使用左外連線效率更高

4.查詢姓李的老師個數：

select count(T#) from Teacher where tname like “李%” 

注：模糊查詢, %代表任意字元，_代表任一單個字元，[……]代表是括號中字元中的單個字元, [^……]代表不是括號中字元中的單個字元

5.查詢沒有學過葉萍老師課的同學學號，姓名：

select studet.s# student.sname 
from student 
where s# not in (select distinct(sc.s#) from sc, course, teacher where sc.c# = course.c# and teacher.t# = course.t# and teacher.tname = “葉萍”)； 

三表聯合 + 子查詢

6.查詢學過001和002課程的同學的姓名學號：

select student.s3 student .sname 
from student join course on student.s# = course.s# 
where(course.c# = ‘001’ union course.c# = ‘002’);

7.查詢學過葉萍老師課的同學的學號，姓名：

select student.s# student.sname 
from student 
where s# in(select distinct(sc.s#) from sc course teacher where sc.c# = course.c# and teacher.t# = course.t# and teacher.tnmae = “葉萍”) 

注：distinct為去重函式

8.查詢002成績比001低的同學的學號，姓名：

select student.s# student .name 
from student where student.s# in(select sc1.s# from sc sc1 join sc sc2 on sc1.s# = sc2.s# where s1.c# = 001 and s2.c# = 002 and sc1.score> sc2.score);

9.查詢所有課程成績小於60分的同學的學號，姓名：

select student.s# student.sname from student join sc on student.s# = sc.s# 
where sc.score > 60;

10.查詢沒有學全 所有課的同學的學號和姓名：

select student.s# student.sname from student,sc 
where student.s# = sc.s# group by student.s#,student.sname having count(c#) < (select count(c#)from course);

11.查詢至少有一門課程與學號1001的同學所學相同的同學的學號和姓名：

select student.s# ,student.sname from student join sc 
where student.s# = sc.s# and c# in select c# from sc where s# = ‘1001’

12.查詢至少學過學號為001同學所有一門課的其他同學的學號和姓名：

select distinct student.s#,student,sname from 
SC join student on SC.s# = student.s# 
where c# in(select c# from sc where s#=’001’);

作者：yexx
來源：雲棲社群