Student(Sid,Sname,Sage,Ssex)學生表

• Sid：學號
• Sname：學生姓名
• Sage：學生年齡
• Ssex：學生性別

Course(Cid,Cname,T#)課程表

• Cid：課程編號
• Cname：課程名稱
• Tid：教師編號

SC(Sid,Cid,score)成績表

• Sid：學號
• Cid：課程編號
• score：成績

Teacher(Tid,Tname)教師表

• Tid：教師編號：
• Tname：教師名字

問題：

1、查詢“001”課程比“002”課程成績高的所有學生的學號

select a.sid from 
(select sid,score from sc where cid
 
='001')a,
(select sid,score from sc where cid='002')b 
where a.sid = b.sid and a.score>b.score;

2、查詢平均成績大於60分的同學的學號和平均成績

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

3、查詢所有同學的學號、姓名、選課數、總成績

select s.sid,s.sname,count_cid as 選課數, 
sum_score  as 總成績
from student s
left join 
(select sid,count(cid) as count_cid,sum(score) as sum_score 
from sc group by sid )sc
on s.sid 
 
= sc.sid;

4、查詢姓‘李’的老師的個數：

select count(tname)
from teacher 
where tname like '李%';

5、查詢沒有學過“葉平”老師可的同學的學號、姓名：

select s.sid,s.sname 
from student as s 
where s.sid not in (
    select DISTINCT sid 
    from sc as sc 
    where sc.cid in (
        select cid 
        from course as c 
        left join teacher as t on c.tid 
 
= t.tid 
        where t.tname = '葉平')
);

6、查詢學過“葉平”老師所教的所有課的同學的學號、姓名：

select s.sid,s.sname 
from student as s 
where s.sid in (
    select distinct sc.sid 
  from sc as sc 
  where sc.cid in (
    select cid 
    from course as c 
    left join teacher as t on c.tid = t.tid 
    where t.tname = '葉平')
        group by sc.sid 
    HAVING count(cid)=
    (select count(cid) 
     from course as c left join teacher as t on c.tid = t.tid 
     where t.tname = '葉平')
);

7、查詢學過“011”並且也學過編號“002”課程的同學的學號、姓名：

SELECT s.sid,s.sname 
from student as s 
left join sc as sc on s.sid = sc.sid
where sc.cid = '001'
and EXISTS(
  select * from sc as sc_2 
  where sc.sid = sc_2.sid 
  and sc_2.cid='002');

select s.sid,s.sname
from student as s 
left join sc as sc 
on sc.sid = s.sid
where sc.cid = '001'
and s.sid in (
  select sid from sc as sc_2 
  where sc_2.cid='002' 
  and sc_2.sid = sc.sid);

8、查詢課程編號“002”的成績比課程編號“001”課程低的所有同學的學號、姓名：

select sid,sname
from (select student.sid,student.sname,score,
     (select score from sc as sc_2 
      where sc_2.sid = student.sid 
      and sc_2.cid = '002') as score2 
      from student,sc 
      where student.sid=sc.sid and cid = '001') s_2
where score2<score;

9、查詢所有課程成績小於60的同學的學號、姓名：

select sid,sname
from student
where sid not in 
(select s.sid 
from student s,sc 
where s.sid=sc.sid and score>60 );

select sid,sname
from student s
where not EXISTS (
select s.sid from sc 
where sc.sid = s.sid and sc.score>60);

10、查詢沒有學全所有課的同學的學號、姓名：

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

select s.sid,s.sname
from student s 
right join sc sc on s.sid = sc.sid
group by s.sid,s.sname
having count(sc.cid)<
(select count(cid) from course);

11、查詢至少有一門課與學號為“1001”同學所學相同的同學的學號和姓名：

select student.sid,sname
from student,sc 
where student.sid = sc.sid
and cid in 
(select cid from sc where sid='1001');

select s.sid,s.sname
from sc sc left join student as s
on sc.sid = s.sid
where sc.cid in (select cid from sc where sid='1001');

select sc_1.sid,s.sname
from sc sc_1 left join student as s
on sc_1.sid = s.sid
where 
exists (select sc_2.cid from sc as sc_2 
where sc_1.cid = sc_2.cid 
and sc_2.sid = '1001');

12、查詢至少學過學號為“001”同學所有一門課的其他同學學號和姓名；

13、把“SC”表中“葉平”老師教的課的成績都更改為此課程的平均成績：

update sc set score = 
(select avg(sc_2.score) from sc sc_2  
where sc_2.cid = sc.cid)
where cid in 
(select c.cid from course c 
left join teacher t on t.tid = c.tid 
where t.tname = '葉平');

14、查詢和“1002”號的同學學習的課程完全相同的其他同學學號和姓名：

select sc_1.sid 
from (select cid from sc where sid='1002')a
left join sc sc_1 on a.cid = sc_1.cid
where sc_1.sid<>'1002' 
group by sc_1.sid 
having count(sc_1.cid) = 
(select count(cid) from sc where sid='1002');

select a.sid,s.sname from 
(select sid,GROUP_CONCAT(cid order by cid separator ',') as cid_str 
from sc where sid='1002')b,
(select sid,GROUP_CONCAT(cid order by cid separator ',') as cid_str 
from sc group by sid)a
left join student s 
on a.sid = s.sid
where a.cid_str = b.cid_str and a.sid<>'1002';

15、刪除學習“葉平”老師課的SC表記錄：

delete from sc WHERE
cid in (
select c.cid from course c 
LEFT JOIN teacher t on c.tid=t.tid 
where t.tname = '葉平');

16、向SC表中插入一些記錄，這些記錄要求符合以下條件：沒有上過編號“003”課程的同學學號、002號課的平均成績：

insert into sc select sid,'002',
(select avg(score) from sc where cid='0022')
from student 
where sid not in (select sid from sc where cid='002');

17、按平均成績從高到低顯示所有學生的“資料庫”、“企業管理”、“英語”三門的課程成績，按如下形式顯示：學生ID，資料庫，企業管理，英語，有效課程數，有效平均分：

select sid as 學生id,
(SELECT score from sc 
where sc.sid = t.sid and cid='004') as 資料庫,
(select score from sc 
where sc.sid = t.sid and cid='001') as 企業管理,
(select score from sc 
where sc.sid = t.sid and cid='015') as 英語,
count(cid) as 有效課程數, avg(t.score) as 平均成績
from sc as t 
group by sid
order by avg(t.score);

18、查詢各科成績最高和最低的分：以如下的形式顯示：課程ID，最高分，最低分

select l.cid as 課程id,l.score as 最高分,
r.score as 最低分
from sc l,sc r
where l.cid = r.cid
and l.score = 
(select max(t.score) from sc t 
where l.cid = t.cid group by t.cid)
and r.score = (select min(t.score) from sc t 
where r.cid = t.cid group by t.cid)
order by l.cid;

select cid as 課程id,max(score) as 最高分,
min(score) as 最低分
from sc 
group by cid;

19、按各科平均成績從低到高和及格率的百分數從高到低順序：

SELECT t.cid as 課程號,
c.cname as 課程名,
COALESCE(avg(score),0) as 平均成績,
100*sum(case 
when COALESCE(score,0)>=60 
then 1 else 0 END)/count(*) as 及格百分數
from sc t
left join course c 
on t.cid = c.cid
group by t.cid
order by 100*sum(case 
when COALESCE(score,0)>=60 
then 1 else 0 END)/count(*);

20、查詢如下課程平均成績和及格率的百分數(用”1行”顯示): 企業管理（001），馬克思（002），OO&UML （003），資料庫（004）：

21、查詢不同老師所教不同課程平均分從高到低顯示：

select t.tid as 教師id,
t.tname as 教師姓名,
sc.cid as 課程id,
avg(score) as 平均成績
from sc as sc
LEFT JOIN course c on sc.cid = c.cid
left join teacher t on c.tid = t.tid
group by sc.cid 
order by avg(sc.score) desc;

22、查詢如下課程成績第3名到第6名的學生成績單：企業管理(001)，馬克思(002)，UML(003)，資料庫(004)：

23、統計下列各科成績，各分數段人數：課程ID，課程名稱，[100-85],[85-70],[70-60],[ 小於60] ：

select sc.cid as 課程id,cname as 課程名稱,
sum(case when score between 85 and 100 then 1 else 0 end) as '[100-85]',
sum(case when score between 70 and 85 then 1 else 0 end) as '[85-70]',
sum(case when score between 60 and 70 then 1 else 0 end) as '[70-60]',
sum(case when score<60 then 1 else 0 end) as '[60-0]'
from sc as sc 
left join course as c
on sc.cid = c.cid
group by sc.cid;

24、查詢學生平均成績及其名次：

select 1+(select count(distinct 平均成績) 
from (select sid,avg(score) as 平均成績 
from sc group by sid)t1 
where 平均成績>t2.平均成績) as 名次,
sid as 學生學號,平均成績 
from (select sid,avg(score) 平均成績 from sc group by sid) as t2
order by 平均成績 desc;

25、查詢各科成績前三名的記錄（不考慮成績並列情況）：

select sid,cid,score
from sc sc_1
where (
select count(3) from sc sc_2 
where sc_1.cid = sc_2.cid 
and sc_2.score>=sc_1.score)<=2 
order by sc_1.cid
);

26、查詢每門課程被選修的學生數：

select cid, count(sid)
from sc 
group by cid;

27、查詢出只選修一門課程的全部學生的學號和姓名：

select sc.sid,s.sname,
count(sc.cid) as 課程數
from sc as sc
LEFT JOIN student as s
on sc.sid = s.sid
group by sc.sid
having count(sc.cid)=1;

28、查詢男生、女生人數：

select count(ssex) as 男生人數
from student
group by ssex
having ssex = '男';
select count(2) from student
where ssex = '女';

29、查詢姓“張”的學生名單：

select sid,sname
from student 
where sname like '張%';

30、查詢同名同姓的學生名單，並統計同名人數：

select sname,count(8)
from student 
group by sname
having count(8)>1;

31、1981年出生的學生名單（注：student表中sage列的型別是datetime）:

32、查詢平均成績大於85的所有學生的學號、姓名和平均成績：

select s.sname,sc.sid,avg(sc.score) as 平均成績
from sc as sc
left join student as s 
on sc.sid = s.sid
group by sc.sid 
having avg(sc.score)>85;

33、查詢每門課程的平均成績，結果按平均成績升序排序，平均成績相同時，按課程號降序排列：

select cid,avg(score)
from sc 
group by cid
order by avg(score),cid desc;

34、查詢課程名稱為“資料庫”，且分數低於60的學生名字和分數：

select c.cname,s.sid,s.sname,sc.score
from course c
left join sc on sc.cid = c.cid
LEFT JOIN student s on s.sid = sc.sid
where c.cname = '資料庫' and sc.score<60;

35、查詢所有學生的選課情況：

select sc.sid,sc.cid,s.sname,c.cname
from sc 
LEFT JOIN course c on sc.cid = c.cid
left join student s on sc.sid = s.sid;

36、查詢任何一門課程成績在70分以上的姓名、課程名稱和分數：

select distinct s.sid,s.sname,sc.cid,sc.score
from sc 
left join student s on sc.sid = s.sid
left join course c on sc.cid = c.cid
where sc.score>70;

37、查詢不及格的課程，並按課程號從大到小的排列：

select cid
from sc 
where score<60
ORDER BY cid;

38、查詢課程編號為“003”且課程成績在80分以上的學生的學號和姓名：

select sc.sid,s.sname 
from sc 
left join student s on sc.sid = s.sid
where sc.cid = '003' and sc.score>80;

39、求選了課程的學生人數：

select count(2) from 
(select distinct sid from sc)a;

40、查詢選修“葉平”老師所授課程的學生中，成績最高的學生姓名及其成績：

select s.sname,sc.score
from sc sc 
left join student s on sc.sid = s.sid
left join course c on sc.cid = c.cid
left join teacher t on c.tid = t.tid
where t.tname = '葉平'
and sc.score = (
select max(score) 
from sc sc_1 
where sc.cid = sc_1.cid);

41、查詢各個課程及相應的選修人數：

select cid,count(*) from sc group by cid;

42、查詢不同課程成績相同的學生和學號、課程號、學生成績：

select DISTINCT a.sid,a.cid,a.score
from sc as a ,sc as b 
where a.score = b.score
and a.cid <> b.cid;

43、查詢每門課程成績最好的前兩名：

44、統計每門課程的學生選修人數(超過10人的課程才統計)。要求輸出課程號和選修人數，查詢結果按人數降序排序，若人數相同，按課程號升序排序：

select cid as 課程號,count(8) as 選修人數
from sc
group by cid
HAVING count(sid)>10
order by count(8) desc,cid;

45、檢索至少選修兩門課程的學生學號：

select sid
from sc
group by sid
having count(8)>=2;

46、查詢全部學生選修的課程和課程號和課程名：

select cid,cname
from course 
where cid in (select cid from sc group by cid);

47、查詢沒學過”葉平”老師講授的任一門課程的學生姓名：

select sname 
from student 
where sid not in (
    select sid 
    from sc,course,teacher 
    where course.tid = teacher.tid and sc.cid = course.cid 
    and teacher.tname='葉平'
);

48、查詢兩門以上不及格課程的同學的學號以及其平均成績：

select sid,avg(COALESCE(score,0))
from sc
where sid in (
    select sid 
    from sc 
    where score<60 
    group by sid 
    having count(8)>2
)
group by sid;

49、檢索“004”課程分數小於60，按分數降序排列的同學學號：

select sid,score
from sc
where cid='004'
and score<60
order by score desc;

50、刪除“002”同學的“001”課程的成績：

delete from sc
where sid = '002'
and cid = '001';

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