Java面试中出现率极高的数据库查询题

经历过面试的程序员都知道，面试过程中面试官可能对你问出千奇百怪的问题，但万变不离其宗，终归也是要问道重点上来，比如像是某一工作的基本操作步骤以及代码的如何编写等等，本文讲的就是最最经典的数据库查询问题。

基本表结构：

teacher(tno,tname) 教师表

student(sno,sname,sage,ssex)学生表

course(cno,cname,tno) 课程表

sc(sno,cno,score) 成绩表

NO.1查询课程1的成绩比课程2的成绩高的所有学生的学号

select a.sno from(select sno,score from sc where cno=1) a,(select sno,score from sc where cno=2) bwhere a.score>b.score and a.sno=b.sno

NO.2查询平均成绩大于60分的同学的学号和平均成绩

select a.sno as "学号", avg(a.score) as "平均成绩" from(select sno,score from sc) a group by sno having avg(a.score)>60

NO.2查询所有同学的学号、姓名、选课数、总成绩

select a.sno as 学号, b.sname as 姓名,count(a.cno) as 选课数, sum(a.score) as 总成绩from sc a, student bwhere a.sno = b.snogroup by a.sno, b.sname

或者：

selectstudent.sno as 学号, student.sname as 姓名, count(sc.cno) as 选课数, sum(score) as 总成绩from student left Outer join sc on student.sno = sc.snogroup by student.sno, sname

NO.3查询姓“张”的老师的个数

selectcount(distinct(tname)) from teacher where tname like '张%‘

或者：

select tname as "姓名", count(distinct(tname)) as "人数" from teacher where tname like'张%'group by tname

NO.4查询没学过“张三”老师课的同学的学号、姓名

select student.sno,student.sname from studentwhere sno not in (select distinct(sc.sno) from sc,course,teacherwhe<span style="color:transparent">来1源gaodai#ma#com搞*代#码1网</span>re sc.cno=course.cno and teacher.tno=course.tno and teacher.tname='张三')

NO.5查询同时学过课程1和课程2的同学的学号、姓名

select sno, sname from studentwhere sno in (select sno from sc where sc.cno = 1)and sno in (select sno from sc where sc.cno = 2)

或者：

selectc.sno, c.sname from(select sno from sc where sc.cno = 1) a,(select sno from sc where sc.cno = 2) b,student cwhere a.sno = b.sno and a.sno = c.sno

或者：

select student.sno,student.sname from student,sc where student.sno=sc.sno and sc.cno=1and exists( select * from sc as sc_2 where sc_2.sno=sc.sno and sc_2.cno=2)

NO.6查询学过“李四”老师所教所有课程的所有同学的学号、姓名

select a.sno, a.sname from student a, sc bwhere a.sno = b.sno and b.cno in(select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四')

或者：

select a.sno, a.sname from student a, sc b,(select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四') ewhere a.sno = b.sno and b.cno = e.cno

NO.7查询课程编号1的成绩比课程编号2的成绩高的所有同学的学号、姓名

<p>select a.sno, a.sname from student a,</p><p>(select sno, score from sc where cno = 1) b,</p><p>(select sno, score from sc where cno = 2) c</p><p>where b.score > c.score and b.sno = c.sno and a.sno = b.sno<br /></p>

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