Oracle 查询练习题

**练习题**
1.各科前三
select * from sc sc1  
where (select count(*) from sc sc2 where sc1.cid=sc2.cid and sc2.score>sc1.score )<=2
内层课程号= 外层课程号
内层分数比外层分数 大的  少于2个  


2.分页查询
select * from
     (
     select rownum rn, empno ,ename ,job ,sal  from 
        (select e.empno ,e.ename ,e.job ,e.sal 
        from emp e  order by nvl(sal,0) desc
        )
    )  t
where t.rn between  5 and 10

3.行列转换
select place,
       sum(decode(sales.name, 'A', sales.sales)) A,
       sum(decode(sales.name, 'B', sales.sales)) B,
       sum(decode(sales.name, 'C', sales.sales)) C
  from sales
  group by place
		查出来之后分组

4.选修相同课程的同学
 
  select sid from stu
 where sid <> (select sid from stu where sname = '小张')
 
 and sid in
       (
        
        (select sid  from record r1
        
          where r1.cid in
                (select cid from record          --小张的 选课的  所有cid
                  where sid = (select sid from stu where sname = '小张')
                )
                
         group by sid
         --count (*) 统计 别人 包含的小张的课 的数量
         having count(*) = (select count(*)  from record       --等于小张的课程数
                            where sid = (select sid from stu where sname = '小张')))
        )
 and sid in
       (select sid from record       --外层套 课程数=小张的sid   count分组      
        group by sid    
        having count(cid) = (select count(*)   from record     --找小张的课程数
                               where sid = (select sid from stu where sname = '小张')
                            )
        )
5.成绩分级
select e.empno,e.ename, e.job ,e.sal ,e.hiredate,
initcap(
decode (sign(sal-801),-1,'e',   
           decode (sign(sal-1601),-1,'d',
                       decode(sign(sal-2501),-1,'c',
                               decode(sign(sal-2801),-1,'b',
                                      decode(sign(sal-3001),-1,'a',
                                             decode(sign(sal-5001),-1,'s')
                                      )  
                               )  
                       )  
                )                                        
       )
       ) "Grade"
        from emp e;

子查询

6.修改张三教授的课程的成绩为对应课程的平均成绩
update sc sc1 
       set score = (select avg(score ) from sc where cid = sc1.cid)
       where cid in 
       (select cid from course 
       where tid in (select tid from teacher where tname ='张三'))


7.相同姓名性别 人数
select sname,ssex,(select count(*)   from student s2 where s2.sname=s.sname and s2.ssex=s.ssex) 人数 from student s where 
(select count(*)   from student s2 where s2.sname=s.sname and s2.ssex=s.ssex)>1



8.不同课程成绩相同的学生
select * from sc sc1 where 
(select count(*) from sc sc2 
where sc1.score=sc2.score 
and sc1.cid<>sc2.cid   --直接排除原记录
group by score
)>0