sql面試-1

--student  info table
create table S (
S#    int not NULL,
SN    varchar(20),
SD    varchar(20)
);

--course table  infoma
create table C(
C#    int not null,
CN    varchar(50),
);

--relation table

create table SC(
S#    int   not null,
C#    int   not null,
Score int  default  0
);



insert into S values(1,'張三','計算機');
insert into S values(2,'李四','軟件');
insert into S values(3,'王五','數據庫');
insert into S values(4,'趙六','計算機');

insert into C values(1,'課程1');
insert into C values(2,'課程2');
insert into C values(3,'課程3');
insert into C values(4,'課程4');
insert into C values(5,'課程5');
insert into C values(6,'課程6');

--delete from sc
insert into SC values(1,1,60);
insert into SC values(1,2,20);
insert into SC values(1,3,60);
insert into SC values(1,4,80);
insert into SC values(1,5,60);
insert into SC values(1,6,60);

insert into SC values(2,1,60);
insert into SC values(2,2,60);
insert into SC values(2,3,40);
insert into SC values(2,4,30);
insert into SC values(2,5,60);

insert into SC values(3,3,60);
--1.查詢出 學了   ‘課程3 ’  的 學生

--1.1

SELECT * FROM S WHERE S# IN
(
        SELECT S# FROM SC WHERE C#=(SELECT C# FROM C  WHERE CN='課程3')
)

--1.2
select S.* from S,C,SC
where S.S#=SC.S# and SC.C#=C.C# and C.CN='課程3';
--1.3
select * from S;
select * from SC;
select * from C;

select s.*
 from s
inner join sc
on s.s#=sc.s#
inner join c
on sc.c#=c.c# and c.cn='課程3'
option(force order)


select s.*
 from s
inner join sc
on s.s#=sc.s#
inner join c
on sc.c#=c.c# and c.cn='課程3'

/*select s.*
 from sc

inner join c
on sc.c#=c.c# --and c.cn='課程3';
inner join s
on s.s#=sc.s#*/

--1.4

Select S# , SN , SD
From S
Where Exists(Select 1
From SC
Inner Join C On C.C#=SC.C#
Where SC.S#=S.S#
)

--2.查詢學了所有課程的學生

--2.1
use d5
SELECT * FROM S
INNER JOIN
(SELECT S#,COUNT(1) _SUM FROM SC GROUP BY S#) AS T1
ON S.S#=T1.S# AND T1._SUM = (SELECT COUNT(1) FROM C)

--2.2
select count(C#) as num from C ;
--MySql
--select S1 ,count(C1) as  num from SC group by S1 having num=(select count(C1) from C);
select * from S
inner join
(select S# ,count(C#) as  num from SC group by S# having count(C#)=(select count(C#) from C)) as t1
 on S.S#= t1.S#;

--2.3最優
Select S.S# , S.SN , S.SD
From S
 Where Not Exists(Select 1
   From C
     Where Not Exists(Select 1
     From SC
     Where SC.C#=C.C#
     And S#=S.S#
    )
)
--3.查詢學了5門以上課程的學生
--3

--最優
Select S.S# , S.SN , S.SD
From S
Inner Join SC On SC.S#=S.S#
Group By S.S#  ,S.SN , S.SD
Having Count(1)>=5


--mysql
Select S.S1 , S.SN , S.SD
From S
Inner Join SC On SC.S1=S.S1
Group By S.S1 
Having Count(1)>=5






--2.查詢有兩門以上不及格的成績的學生,學好，姓名，
-- <60的學生
select * from sc

 select S# ,C#, Score,count(S#) ss from SC
  group by S#,C# ,Score having   Score<60
--注意count(S#) 統計的是 group by S#,C# 後的信息,只顯示一行



SELECT S.S# ,S.SN FROM S
, ( select S# ,C#,Score ss from SC
  group by S#,C# ,Score having  Score<60 ) AS T1
where S.S#= T1.S# group by S.S#,S.SN having count(ss)>=2

--group by 有一個原則,就是 select 後面的所有列中,沒有使用聚合函數的列,必須出現在 group by 後面

--mysql
select S1 ,C1,Score from SC
 where  Score<60  group by S1,C1 ,Score having count(S1)>=2


select S.S#,S.SN,S.SD
 from S
 inner join SC On SC.S#=S.S# group by S.S#
  having count(SC.C#)

--3.如果讓你建索引,你會在哪建


--4.統計一個學生成績報表的思路
--表報格式如下
--學號        課程1       課程2    課程3   ...
--001         100         100       100
--002         100         100       100
--...             【 學號和課程都可變  】


--method 1 固定死的，如果需求一變動，就需要改代碼。
select SC.S# as 學號 ,
 S.SN  as 姓名,
 max(case when SC.C#=1 then SC.Score end ) as 課程1,
 max(case when SC.C#=2 then SC.Score end) as 課程2,
 max(case when SC.C#=3 then SC.Score end) as 課程3,
 max(case when SC.C#=4 then SC.Score end) as 課程4
from SC,S where SC.S#=S.S# group by SC.s#,S.SN


--method 2

DECLARE @sql varchar(8000)
set @sql=''
select @sql=@sql+',max(case when sc.c#='''+Convert(varchar,sc.C#)+''' then sc.score end) ['+Convert(varchar,c.cn)+']'
       from sc,c WHERE sc.C# = c.c# group by sc.c#,c.cn
set @sql=stuff(@sql,1,1,'')

PRINT @sql
exec ('select max(s.sn) as [Name],'+@sql+' from sc,s where sc.s# = s.s# group by sc.s#')



DECLARE @s varchar(8000)
set @s=''
select @s=@s+',max(case when sc.c#='+Convert(varchar,sc.C#)+' then sc.score end) as '+convert(varchar,c.cn)
  from sc,c where sc.c#=c.c# group by sc.c#,c.cn
set @s=stuff(@s,1,1,'')
PRINT @s
exec('select max(s.sn) as name ,'+@s+' from sc,s where sc.s#=s.s# group by sc.s#')