數據庫MySQL經典面試題之SQL語句

數據庫MySQL經典面試題之SQL語句

1.須要數據庫表1.學生表
Student(SID,Sname,Sage,Ssex) --SID 學生編號,Sname 學生姓名,Sage 出生年月,Ssex 學生性別

2.課程表
Course(CID,Cname,TID) --CID --課程編號,Cname 課程名稱,TID 教師編號
3.教師表
Teacher(TID,Tname) --TID 教師編號,Tname 教師姓名
4.成績表
SC(SID,CID,score) --SID 學生編號,CID 課程編號,score 分數

添加測試數據1.學生表
create table Student(SID varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10));
insert into Student values('01' , '趙雷' , '1990-01-01' , '男');
insert into Student values('02' , '錢電' , '1990-12-21' , '男');
insert into Student values('03' , '孫風' , '1990-05-20' , '男');
insert into Student values('04' , '李雲' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吳蘭' , '1992-03-01' , '女');
insert into Student values('07' , '鄭竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');

2.課程表
create table Course(CID varchar(10),Cname nvarchar(10),TID varchar(10));
insert into Course values('01' , '語文' , '02');
insert into Course values('02' , '數學' , '01');
insert into Course values('03' , '英語' , '03');

3.教師表
create table Teacher(TID varchar(10),Tname nvarchar(10));
insert into Teacher values('01' , '張三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

4.成績表
create table SC(SID varchar(10),CID varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

--一、查詢"01"課程比"02"課程成績高的學生的信息及課程分數

--1.一、查詢同時存在"01"課程和"02"課程的狀況
select a.* , b.score 課程01的分數,c.score 課程02的分數 from Student a , SC b , SC c
where a.SID = b.SID and a.SID = c.SID and b.CID = '01' and c.CID = '02' and b.score > c.score

--1.二、查詢同時存在"01"課程和"02"課程的狀況和存在"01"課程但可能不存在"02"課程的狀況(不存在時顯示爲null)(如下存在相同內容時再也不解釋)
select a.* , b.score 課程01的分數,c.score 課程02的分數 from Student a
left join SC b on a.SID = b.SID and b.CID = '01'
left join SC c on a.SID = c.SID and c.CID = '02'
where b.score > isnull(c.score)

--二、查詢"01"課程比"02"課程成績低的學生的信息及課程分數

--2.一、查詢同時存在"01"課程和"02"課程的狀況
select a.* , b.score 課程01的分數 ,c.score 課程02的分數 from Student a , SC b , SC c
where a.SID = b.SID and a.SID = c.SID and b.CID = '01' and c.CID = '02' and b.score < c.score

--2.二、查詢同時存在"01"課程和"02"課程的狀況和不存在"01"課程但存在"02"課程的狀況
select a.* , b.score 課程01的分數 ,c.score 課程02的分數 from Student a
left join SC b on a.SID = b.SID and b.CID = '01'
left join SC c on a.SID = c.SID and c.CID = '02'
where isnull(b.score,0) < c.score

--三、查詢平均成績大於等於60分的同窗的學生編號和學生姓名和平均成績
select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.SID = b.SID
group by a.SID , a.Sname
having cast(avg(b.score) as decimal(18,2)) >= 60
order by a.SID

--四、查詢平均成績小於60分的同窗的學生編號和學生姓名和平均成績

--4.一、查詢在sc表存在成績的學生信息的SQL語句。
select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.SID = b.SID
group by a.SID , a.Sname
having cast(avg(b.score) as decimal(18,2)) < 60
order by a.SID

--4.二、查詢在sc表中不存在成績的學生信息的SQL語句。
select a.SID , a.Sname , isnull(cast(avg(b.score) as decimal(18,2)),0) avg_score
from Student a left join sc b
on a.SID = b.SID
group by a.SID , a.Sname
having isnull(cast(avg(b.score) as decimal(18,2)),0) < 60
order by a.SID

--五、查詢全部同窗的學生編號、學生姓名、選課總數、全部課程的總成績

--5.一、查詢全部有成績的SQL。
select a.SID 學生編號 , a.Sname 學生姓名 , count(b.CID) 選課總數, sum(score) 全部課程的總成績
from Student a , SC b
where a.SID = b.SID
group by a.SID,a.Sname
order by a.SID

--5.二、查詢全部(包括有成績和無成績)的SQL。
select a.SID 學生編號 , a.Sname 學生姓名 , count(b.CID) 選課總數, sum(score) 全部課程的總成績
from Student a left join SC b
on a.SID = b.SID
group by a.SID,a.Sname
order by a.SID

--六、查詢"李"姓老師的數量
--方法1
select count(Tname) 李姓老師的數量 from Teacher where Tname like '李%'
--方法2
select count(Tname) 李姓老師的數量 from Teacher where left(Tname,1) = '李'

--七、查詢學過"張三"老師授課的同窗的信息
select distinct Student.* from Student , SC , Course , Teacher
where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '張三'
order by Student.SID

--八、查詢沒學過"張三"老師授課的同窗的信息
select m.* from Student m where SID not in (select distinct SC.SID from SC , Course , Teacher where SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '張三') order by m.SID

--九、查詢學過編號爲"01"而且也學過編號爲"02"的課程的同窗的信息
--方法1
select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID
--方法2
select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '02' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '01') order by Student.SID
--方法3
select m.* from Student m where SID in
(
select SID from
(
select distinct SID from SC where CID = '01'

union all

select distinct SID from SC where CID = '02'

) t group by SID having count(1) = 2

)

order by m.SID

--十、查詢學過編號爲"01"可是沒有學過編號爲"02"的課程的同窗的信息

--方法1

select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and not exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID

--方法2
select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '01' and Student.SID not in (Select SC_2.SID from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02') order by Student.SID

--十一、查詢沒有學全全部課程的同窗的信息
--11.一、
select Student.*
from Student , SC
where Student.SID = SC.SID
group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

--11.2
select Student.*
from Student left join SC
on Student.SID = SC.SID
group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

--十二、查詢至少有一門課與學號爲"01"的同窗所學相同的同窗的信息
select distinct Student.* from Student , SC where Student.SID = SC.SID and SC.CID in (select CID from SC where SID = '01') and Student.SID <> '01'

--1三、查詢和"01"號的同窗學習的課程徹底相同的其餘同窗的信息
select Student.* from Student where SID in
(select distinct SC.SID from SC where SID <> '01' and SC.CID in (select distinct CID from SC where SID = '01')
group by SC.SID having count(1) = (select count(1) from SC where SID='01'))

--1四、查詢沒學過"張三"老師講授的任一門課程的學生姓名
select student.* from student where student.SID not in
(select distinct sc.SID from sc , course , teacher where sc.CID = course.CID and course.TID = teacher.TID and teacher.tname = '張三')
order by student.SID

--1五、查詢兩門及其以上不及格課程的同窗的學號，姓名及其平均成績
select student.SID , student.sname , cast(avg(score) as decimal(18,2)) avg_score from student , sc
where student.SID = SC.SID and student.SID in (select SID from SC where score < 60 group by SID having count(1) >= 2)
group by student.SID , student.sname

--1六、檢索"01"課程分數小於60，按分數降序排列的學生信息
select student.* , sc.CID , sc.score from student , sc
where student.SID = SC.SID and sc.score < 60 and sc.CID = '01'
order by sc.score desc

--1七、按平均成績從高到低顯示全部學生的全部課程的成績以及平均成績--17.1 SQL 2000 靜態
select a.SID 學生編號 , a.Sname 學生姓名 ,
max(case c.Cname when '語文' then b.score else null end) 語文 ,
max(case c.Cname when '數學' then b.score else null end) 數學 ,
max(case c.Cname when '英語' then b.score else null end) 英語 ,
cast(avg(b.score) as decimal(18,2)) 平均分
from Student a
left join SC b on a.SID = b.SID
left join Course c on b.CID = c.CID
group by a.SID , a.Sname
order by 平均分 desc

--17.2 SQL 2000 動態
declare @sql nvarchar(4000)
set @sql = 'select a.SID ' + '學生編號' + ' , a.Sname ' + '學生姓名'
select @sql = @sql + ',max(case c.Cname when '''+Cname+''' then b.score else null end) '+Cname+' '
from (select distinct Cname from Course) as t
set @sql = @sql + ' , cast(avg(b.score) as decimal(18,2)) ' + '平均分' + ' from Student a left join SC b on a.SID = b.SID left join Course c on b.CID = c.CID
group by a.SID , a.Sname order by ' + '平均分' + ' desc'
exec(@sql)

--1八、查詢各科成績最高分、最低分和平均分：以以下形式顯示：課程ID，課程name，最高分，最低分，平均分，及格率，中等率，優良率，優秀率
--及格爲>=60，中等爲：70-80，優良爲：80-90，優秀爲：>=90

--方法1
select m.CID 課程編號 , m.Cname 課程名稱 ,
max(n.score) 最高分 ,
min(n.score) 最低分 ,
cast(avg(n.score) as decimal(18,2)) 平均分 ,
cast((select count(1) from SC where CID = m.CID and score >= 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 及格率 ,
cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 中等率 ,
cast((select count(1) from SC where CID = m.CID and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 優良率 ,
cast((select count(1) from SC where CID = m.CID and score >= 90)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 優秀率
from Course m , SC n
where m.CID = n.CID
group by m.CID , m.Cname
order by m.CID

--方法2
select m.CID 課程編號 , m.Cname 課程名稱 ,
(select max(score) from SC where CID = m.CID) 最高分 ,
(select min(score) from SC where CID = m.CID) 最低分 ,
(select cast(avg(score) as decimal(18,2)) from SC where CID = m.CID) 平均分 ,
cast((select count(1) from SC where CID = m.CID and score >= 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 及格率,
cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 80 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 中等率 ,
cast((select count(1) from SC where CID = m.CID and score >= 80 and score < 90 )*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 優良率 ,
cast((select count(1) from SC where CID = m.CID and score >= 90)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 優秀率
from Course m
order by m.CID

--1九、按各科成績進行排序，並顯示排名--19.1 sql 2000用子查詢完成

--Score重複時保留名次空缺
select t.* , px = (select count(1) from SC where CID = t.CID and score > t.score) + 1 from sc t order by t.cid , px

--Score重複時合併名次
select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t order by t.cid , px

--19.2 sql 2005用rank,DENSE_RANK完成

--Score重複時保留名次空缺(rank完成)
select t.* , px = rank() over(partition by cid order by score desc) from sc t order by t.CID , px

--Score重複時合併名次(DENSE_RANK完成)
select t.* , px = DENSE_RANK() over(partition by cid order by score desc) from sc t order by t.CID , px

--20、查詢學生的總成績並進行排名--20.1 查詢學生的總成績
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
order by 總成績 desc

--20.2 查詢學生的總成績並進行排名，sql 2000用子查詢完成，分總分重複時保留名次空缺和不保留名次空缺兩種。
select t1.* , px = (select count(1) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t2 where 總成績 > t1.總成績) + 1 from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t1
order by px
select t1.* , px = (select count(distinct 總成績) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t2 where 總成績 >= t1.總成績) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t1
order by px

--20.3 查詢學生的總成績並進行排名，sql 2005用rank,DENSE_RANK完成，分總分重複時保留名次空缺和不保留名次空缺兩種。
select t.* , px = rank() over(order by 總成績 desc) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t
order by px
select t.* , px = DENSE_RANK() over(order by 總成績 desc) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(sum(score),0) 總成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t
order by px

--2一、查詢不一樣老師所教不一樣課程平均分從高到低顯示
select m.TID , m.Tname , cast(avg(o.score) as decimal(18,2)) avg_score
from Teacher m , Course n , SC o
where m.TID = n.TID and n.CID = o.CID
group by m.TID , m.Tname
order by avg_score desc

--2二、查詢全部課程的成績第2名到第3名的學生信息及該課程成績--22.1 sql 2000用子查詢完成
--Score重複時保留名次空缺
select * from (select t.* , px = (select count(1) from SC where CID = t.CID and score > t.score) + 1 from sc t) m where px between 2 and 3 order by m.cid , m.px

--Score重複時合併名次
select * from (select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t) m where px between 2 and 3 order by m.cid , m.px

--22.2 sql 2005用rank,DENSE_RANK完成

--Score重複時保留名次空缺(rank完成)
select * from (select t.* , px = rank() over(partition by cid order by score desc) from sc t) m where px between 2 and 3 order by m.CID , m.px

--Score重複時合併名次(DENSE_RANK完成)
select * from (select t.* , px = DENSE_RANK() over(partition by cid order by score desc) from sc t) m where px between 2 and 3 order by m.CID , m.px

--2三、統計各科成績各分數段人數：課程編號,課程名稱, 100-85 , 85-70 , 70-60 , 0-60 及所佔百分比 --23.1 統計各科成績各分數段人數：課程編號,課程名稱, 100-85 , 85-70 , 70-60 , 0-60

--橫向顯示
select Course.CID 課程編號 , Cname as 課程名稱 ,
sum(case when score >= 85 then 1 else 0 end) 85-100 ,
sum(case when score >= 70 and score < 85 then 1 else 0 end) 70-85 ,
sum(case when score >= 60 and score < 70 then 1 else 0 end) 60-70 ,
sum(case when score < 60 then 1 else 0 end) 0-60
from sc , Course
where SC.CID = Course.CID
group by Course.CID , Course.Cname
order by Course.CID

--縱向顯示1(顯示存在的分數段)
select m.CID 課程編號 , m.Cname 課程名稱 , 分數段 = (
case when n.score >= 85 then '85-100'
when n.score >= 70 and n.score < 85 then '70-85'
when n.score >= 60 and n.score < 70 then '60-70'
else '0-60'
end) ,
count(1) 數量
from Course m , sc n
where m.CID = n.CID
group by m.CID , m.Cname , (
case when n.score >= 85 then '85-100'
when n.score >= 70 and n.score < 85 then '70-85'
when n.score >= 60 and n.score < 70 then '60-70'
else '0-60'
end)
order by m.CID , m.Cname , 分數段

--縱向顯示2(顯示存在的分數段，不存在的分數段用0顯示)

select m.CID 課程編號 , m.Cname 課程名稱 , 分數段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 數量

from Course m , sc n

where m.CID = n.CID

group by all m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分數段

--23.2 統計各科成績各分數段人數：課程編號,課程名稱, 100-85 , 85-70 , 70-60 , <60 及所佔百分比

--橫向顯示

select m.CID 課程編號, m.Cname 課程名稱,

(select count(1) from SC where CID = m.CID and score < 60) 0-60 ,

cast((select count(1) from SC where CID = m.CID and score < 60)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 60 and score < 70) 60-70 ,

cast((select count(1) from SC where CID = m.CID and score >= 60 and score < 70)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 70 and score < 85) 70-85 ,

cast((select count(1) from SC where CID = m.CID and score >= 70 and score < 85)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比 ,

(select count(1) from SC where CID = m.CID and score >= 85) 85-100 ,

cast((select count(1) from SC where CID = m.CID and score >= 85)*100.0 / (select count(1) from SC where CID = m.CID) as decimal(18,2)) 百分比

from Course m

order by m.CID

--縱向顯示1(顯示存在的分數段)

select m.CID 課程編號 , m.Cname 課程名稱 , 分數段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 數量 ,

cast(count(1) * 100.0 / (select count(1) from sc where CID = m.CID) as decimal(18,2)) 百分比

from Course m , sc n

where m.CID = n.CID

group by m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分數段

--縱向顯示2(顯示存在的分數段，不存在的分數段用0顯示)

select m.CID 課程編號 , m.Cname 課程名稱 , 分數段 = (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end) ,

count(1) 數量 ,

cast(count(1) * 100.0 / (select count(1) from sc where CID = m.CID) as decimal(18,2)) 百分比

from Course m , sc n

where m.CID = n.CID

group by all m.CID , m.Cname , (

case when n.score >= 85 then '85-100'

when n.score >= 70 and n.score < 85 then '70-85'

when n.score >= 60 and n.score < 70 then '60-70'

else '0-60'

end)

order by m.CID , m.Cname , 分數段

--2四、查詢學平生均成績及其名次--24.1 查詢學生的平均成績並進行排名，sql 2000用子查詢完成，分平均成績重複時保留名次空缺和不保留名次空缺兩種。

select t1.* , px = (select count(1) from

(

select m.SID 學生編號 ,

m.Sname 學生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成績

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 平均成績 > t1.平均成績) + 1 from

(

select m.SID 學生編號 ,

m.Sname 學生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成績

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

select t1.* , px = (select count(distinct 平均成績) from

(

select m.SID 學生編號 ,

m.Sname 學生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成績

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t2 where 平均成績 >= t1.平均成績) from

(

select m.SID 學生編號 ,

m.Sname 學生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成績

from Student m left join SC n on m.SID = n.SID

group by m.SID , m.Sname

) t1

order by px

--24.2 查詢學生的平均成績並進行排名，sql 2005用rank,DENSE_RANK完成，分平均成績重複時保留名次空缺和不保留名次空缺兩種。

select t.* , px = rank() over(order by 平均成績 desc) from

(

select m.SID 學生編號 ,

m.Sname 學生姓名 ,

isnull(cast(avg(score) as decimal(18,2)),0) 平均成績

from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t
order by px
select t.* , px = DENSE_RANK() over(order by 平均成績 desc) from
(
select m.SID 學生編號 ,
m.Sname 學生姓名 ,
isnull(cast(avg(score) as decimal(18,2)),0) 平均成績
from Student m left join SC n on m.SID = n.SID
group by m.SID , m.Sname
) t
order by px

--2五、查詢各科成績前三名的記錄--25.1 分數重複時保留名次空缺
select m.* , n.CID , n.score from Student m, SC n where m.SID = n.SID and n.score in
(select top 3 score from sc where CID = n.CID order by score desc) order by n.CID , n.score desc

--25.2 分數重複時不保留名次空缺，合併名次

--sql 2000用子查詢實現
select * from (select t.* , px = (select count(distinct score) from SC where CID = t.CID and score >= t.score) from sc t) m where px between 1 and 3 order by m.Cid , m.px

--sql 2005用DENSE_RANK實現
select * from (select t.* , px = DENSE_RANK() over(partition by Cid order by score desc) from sc t) m where px between 1 and 3 order by m.CID , m.px

--2六、查詢每門課程被選修的學生數
select Cid , count(SID) 學生數 from sc group by CID

--2七、查詢出只有兩門課程的所有學生的學號和姓名
select Student.SID , Student.Sname
from Student , SC
where Student.SID = SC.SID
group by Student.SID , Student.Sname
having count(SC.CID) = 2
order by Student.SID

--2八、查詢男生、女生人數
select count(Ssex) as 男生人數 from Student where Ssex = N'男'
select count(Ssex) as 女生人數 from Student where Ssex = N'女'
select sum(case when Ssex = N'男' then 1 else 0 end) 男生人數 ,sum(case when Ssex = N'女' then 1 else 0 end) 女生人數 from student
select case when Ssex = N'男' then N'男生人數' else N'女生人數' end 男女狀況 , count(1) 人數 from student group by case when Ssex = N'男' then N'男生人數' else N'女生人數' end

--2九、查詢名字中含有"風"字的學生信息
select * from student where sname like N'%風%'
select * from student where charindex(N'風' , sname) > 0

--30、查詢同名同性學生名單，並統計同名人數
select Sname 學生姓名 , count(*) 人數 from Student group by Sname having count(*) > 1

--3一、查詢1990年出生的學生名單(注：Student表中Sage列的類型是datetime)
select * from Student where year(sage) = 1990
select * from Student where datediff(yy,sage,'1990-01-01') = 0
select * from Student where datepart(yy,sage) = 1990
select * from Student where convert(varchar(4),sage,120) = '1990'

--3二、查詢每門課程的平均成績，結果按平均成績降序排列，平均成績相同時，按課程編號升序排列
select m.CID , m.Cname , cast(avg(n.score) as decimal(18,2)) avg_score
from Course m, SC n
where m.CID = n.CID
group by m.CID , m.Cname
order by avg_score desc, m.CID asc

--3三、查詢平均成績大於等於85的全部學生的學號、姓名和平均成績
select a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.SID = b.SID
group by a.SID , a.Sname
having cast(avg(b.score) as decimal(18,2)) >= 85
order by a.SID

--3四、查詢課程名稱爲"數學"，且分數低於60的學生姓名和分數
select sname , score
from Student , SC , Course
where SC.SID = Student.SID and SC.CID = Course.CID and Course.Cname = N'數學' and score < 60

--3五、查詢全部學生的課程及分數狀況
select Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course
where Student.SID = SC.SID and SC.CID = Course.CID
order by Student.SID , SC.CID

--3六、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 Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course
where Student.SID = SC.SID and SC.CID = Course.CID and SC.score >= 70
order by Student.SID , SC.CID

--3七、查詢不及格的課程
select Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course
where Student.SID = SC.SID and SC.CID = Course.CID and SC.score < 60
order by Student.SID , SC.CID

--3八、查詢課程編號爲01且課程成績在80分以上的學生的學號和姓名
select Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course
where Student.SID = SC.SID and SC.CID = Course.CID and SC.CID = '01' and SC.score >= 80
order by Student.SID , SC.CID

--3九、求每門課程的學生人數
select Course.CID , Course.Cname , count(*) 學生人數
from Course , SC
where Course.CID = SC.CID
group by Course.CID , Course.Cname
order by Course.CID , Course.Cname

--40、查詢選修"張三"老師所授課程的學生中，成績最高的學生信息及其成績--40.1 當最高分只有一個時
select top 1 Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course , Teacher
where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'張三'
order by SC.score desc

--40.2 當最高分出現多個時
select Student.* , Course.Cname , SC.CID , SC.score
from Student, SC , Course , Teacher
where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'張三' and
SC.score = (select max(SC.score) from SC , Course , Teacher where SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = N'張三')

--4一、查詢不一樣課程成績相同的學生的學生編號、課程編號、學生成績
--方法1
select m.* from SC m ,(select CID , score from SC group by CID , score having count(1) > 1) n
where m.CID= n.CID and m.score = n.score order by m.CID , m.score , m.SID

--方法2
select m.* from SC m where exists (select 1 from (select CID , score from SC group by CID , score having count(1) > 1) n
where m.CID= n.CID and m.score = n.score) order by m.CID , m.score , m.SID

--4二、查詢每門功成績最好的前兩名
select t.* from sc t where score in (select top 2 score from sc where CID = T.CID order by score desc) order by t.CID , t.score desc

--4三、統計每門課程的學生選修人數（超過5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列，若人數相同，按課程號升序排列
select Course.CID , Course.Cname , count(*) 學生人數
from Course , SC
where Course.CID = SC.CID
group by Course.CID , Course.Cname
having count(*) >= 5
order by 學生人數 desc , Course.CID

--4四、檢索至少選修兩門課程的學生學號
select student.SID , student.Sname
from student , SC
where student.SID = SC.SID
group by student.SID , student.Sname
having count(1) >= 2
order by student.SID

--4五、查詢選修了所有課程的學生信息
--方法1 根據數量來完成
select student.* from student where SID in
(select SID from sc group by SID having count(1) = (select count(1) from course))

--方法2 使用雙重否認來完成
select t.* from student t where t.SID not in
(
select distinct m.SID from
(
select SID , CID from student , course
) m where not exists (select 1 from sc n where n.SID = m.SID and n.CID = m.CID)
)

--方法3 使用雙重否認來完成
select t.* from student t where not exists(select 1 from
(
select distinct m.SID from
(
select SID , CID from student , course
) m where not exists (select 1 from sc n where n.SID = m.SID and n.CID = m.CID)
) k where k.SID = t.SID
)

--4六、查詢各學生的年齡--46.1 只按照年份來算
select * , datediff(yy , sage , getdate()) 年齡 from student

--46.2 按照出生日期來算，當前月日 < 出生年月的月日則，年齡減一
select * , case when right(convert(varchar(10),getdate(),120),5) < right(convert(varchar(10),sage,120),5) then datediff(yy , sage , getdate()) - 1 else datediff(yy , sage , getdate()) end 年齡 from student

--4七、查詢本週過生日的學生
select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--4八、查詢下週過生日的學生
select * from student where datediff(week,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1

--4九、查詢本月過生日的學生
select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = 0

--50、查詢下月過生日的學生
select * from student where datediff(mm,datename(yy,getdate()) + right(convert(varchar(10),sage,120),6),getdate()) = -1