• 16、按平均成績從低到高顯示所有學生的“語文”、“數學”、“英語”三門的課程成績，
  按如下形式顯示： 學生ID,語文,數學,英語,有效課程數,有效平均分；

select t.sid as ‘學生ID‘,
(select score from sc where sid=t.sid and cid=‘002‘) as ‘語文‘,
(select score from sc where sid=t.sid and cid=‘003‘) as ‘數學‘,
(select score from sc where sid=t.sid and cid=‘004‘) as ‘英語‘,
count(t.cid) as ‘有效課程數‘,
avg(t.score) as ‘有效平均分‘
from sc t
group by t.sid
order by avg(t.score);
 

• 17、查詢各科成績最高和最低的分：以如下形式顯示：課程ID，最高分，最低分；

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

• 18、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 sc.cid,c.cname,round(IFNULL(avg(sc.score),0),2) as ‘平均成績‘,
round(100*sum(case when ifnull(sc.score,0)>=60 then 1 else 0 end)/count(*),2) as ‘及格率‘
from sc sc,course c
where sc.cid=c.cid
group by 1,2
order by ‘及格率‘ desc;
 

• 19、查詢如下課程平均成績和及格率的百分數(備註：需要在1行內顯示):
  企業管理（002），OO&UML （003），數據庫（004）

select
sum(case when cid=‘002‘ then score else 0 end)/sum(case when cid=‘002‘ then 1 else 0 end) as ‘企業管理平均分‘,
sum(case when cid=‘002‘ and score>=60 then 1 else 0 end)/sum(case when cid=‘002‘ then 1 else 0 end) as ‘企業管理及格率‘,
sum(case when cid=‘003‘ then score else 0 end)/sum(case when cid=‘003‘ then 1 else 0 end) as ‘OO&UML平均分‘,
sum(case when cid=‘003‘ and score>=60 then 1 else 0 end)/sum(case when cid=‘003‘ then 1 else 0 end) as ‘OO&UML及格率‘,
sum(case when cid=‘004‘ then score else 0 end)/sum(case when cid=‘004‘ then 1 else 0 end) as ‘數據庫平均分‘,
sum(case when cid=‘004‘ and score>=60 then 1 else 0 end)/sum(case when cid=‘004‘ then 1 else 0 end) as ‘數據庫及格率‘
from sc;
 

• 20、查詢不同老師所教不同課程平均分從高到低顯示；

select c.cid,max(c.cname) as ‘cname‘,max(t.tid) as ‘tid‘,max(t.tname) as ‘tname‘,
avg(score) as ‘avgscore‘
from sc sc,course c,teacher t
where sc.cid=c.cid and c.tid=t.tid
group by c.cid
order by avgscore desc;

• 21、統計列印各科成績,各分數段人數:課程ID,課程名稱,[100-85],[85-70],[70-60],[ <60]

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

• 22、查詢學生平均成績及其名次；

select s.Sid,s.Sname,T2.AvgScore,
    (select COUNT(AvgScore) from 
    (select Sid,AVG(Score) as ‘AvgScore‘ from SC group by Sid) as T1 
    where T2.AvgScore<T1.AvgScore)+1 as ‘Rank‘
from 
    (select Sid,AVG(Score) as ‘AvgScore‘ from SC
    group by Sid) as T2,
    Student s
where s.Sid=T2.Sid
order by AvgScore desc

• 23、查詢各科成績前三名的記錄:(不考慮成績並列情況)

select sc.cid,c.cname,sc.sid,s.sname,sc.score
from student s,sc sc,course c
where sc.cid=c.cid and sc.sid=s.sid and sc.score in
(
    select score from sc sc2
    where sc.cid=sc2.cid
    order by score desc
)
order by sc.cid,sc.Score desc

• 24、查詢每門課程被選修的學生數；

select sc.cid,max(c.cname) as ‘CNAME‘,count(distinct sc.sid) as ‘studentCount‘
from sc sc,course c
where sc.cid=c.cid
group by sc.cid;

• 25、查詢出只選修了一門課程的全部學生的學號和姓名；

select s.sid,s.sname
from student s
where s.sid in
(select sc.sid from sc sc
    group by sc.sid
    having count(distinct sc.cid)=3)

• 26、查詢男生、女生的人數

select COUNT(sid) as ‘BoysCount‘ from Student s where s.Ssex=‘男‘;
select COUNT(sid) as ‘GirlsCount‘ from Student s where s.Ssex=‘女‘

• 27、查詢姓“張”的學生名單；

select s.sid,s.Sname 
from Student s 
where s.Sname like ‘張%‘

• 28、查詢同名同姓學生名單，並統計同名人數；

select s.Sname,COUNT(Sname) as ‘SameCount‘
from Student s
group by s.Sname
having COUNT(Sname)>1

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

select sc.cid,AVG(sc.Score) as ‘AvgScore‘ 
from SC sc
group by sc.cid
order by AvgScore asc,cid desc

• 30、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 sc.sid,s.Sname,AVG(sc.Score) as ‘AvgScore‘ 
from Student s,SC sc
where s.sid=sc.sid
group by sc.sid,s.Sname
having AVG(sc.Score)>85

• 31、查詢課程名稱為“數學”，且分數低於60的學生姓名和分數

select s.Sname,sc.Score from Student s,SC sc,Course c
where s.Sid=sc.Sid and sc.Cid=c.Cid and c.Cname=‘數學‘ and sc.Score<60

• 32、查詢所有學生的選課情況；

select s.Sid,s.Sname,c.Cid,c.Cname from Student s,SC sc,Course c
where s.Sid=sc.Sid and c.Cid=sc.Cid
order by s.Sid

• 33、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,c.cname,sc.score
from student s,sc sc,course c
where s.sid=sc.sid and sc.cid=c.cid and sc.score>=70;

• 34、查詢不及格的課程，並按課程號從大到小排列；

select distinct sc.cid,c.cname from sc sc,course c
where sc.cid=c.cid and sc.score<60
order by sc.cid desc;

• 35、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,sc.score
from student s,sc sc
where s.sid=sc.sid and sc.cid=‘003‘ and sc.score>=80;

• 36、求選了課程的學生人數（超簡單的一題）

select count(distinct sid) as ‘studentCount‘ from sc;

• 37、查詢選修“楊艷”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.sid,s.sname,sc.score
from student s,sc sc,course c,teacher t
where s.sid=sc.sid and sc.cid=c.cid and c.tid=t.tid and t.tname=‘楊艷‘
and sc.score=
(
    select max(sc2.score) from sc sc2 where sc.cid=sc2.cid
)

文章轉載自https://www.cnblogs.com/edisonchou/p/3878135.html
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