Oracle 查詢練習題

**練習題**
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
內層課程號= 外層課程號
內層分數比外層分數 大的  少於2個  


2.分頁查詢
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.行列轉換
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
		查出來之後分組

4.選修相同課程的同學
 
  select sid from stu
 where sid <> (select sid from stu where sname = '小張')
 
 and sid in
       (
        
        (select sid  from record r1
        
          where r1.cid in
                (select cid from record          --小張的 選課的  所有cid
                  where sid = (select sid from stu where sname = '小張')
                )
                
         group by sid
         --count (*) 統計 別人 包含的小張的課 的數量
         having count(*) = (select count(*)  from record       --等於小張的課程數
                            where sid = (select sid from stu where sname = '小張')))
        )
 and sid in
       (select sid from record       --外層套 課程數=小張的sid   count分組      
        group by sid    
        having count(cid) = (select count(*)   from record     --找小張的課程數
                               where sid = (select sid from stu where sname = '小張')
                            )
        )
5.成績分級
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;

子查詢

6.修改張三教授的課程的成績爲對應課程的平均成績
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 ='張三'))


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



8.不同課程成績相同的學生
select * from sc sc1 where 
(select count(*) from sc sc2 
where sc1.score=sc2.score 
and sc1.cid<>sc2.cid   --直接排除原記錄
group by score
)>0