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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 student where sno not in (select distinct(sc.sno) from sc,course,teacher where 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
select a.sno, a.sname from student a,
(select sno, score from sc where cno = 1) b,
(select sno, score from sc where cno = 2) c
where b.score > c.score and b.sno = c.sno and a.sno = b.sno
NO.8查询所有课程成绩小于60分的同学的学号、姓名
select sno,sname from studentwhere sno not in (select distinct sno from sc where score > 60)
NO.9查询至少有一门课程与学号为1的同学所学课程相同的同学的学号和姓名
select distinct a.sno, a.snamefrom student a, sc bwhere a.sno <> 1 and a.sno=b.sno andb.cno in (select cno from sc where sno = 1)
或者：
select s.sno,s.sname from student s,(select sc.sno from scwhere sc.cno in (select sc1.cno from sc sc1 where sc1.sno=1)and sc.sno<>1group by sc.sno)r1where r1.sno=s.sno
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