sql server04

use MyScool
--全局变量 = 系统变量
--print  @@version
--select  @@VERSION
--定义局部变量=自定义变量
--declare   @age   int
--赋值的方式  set   select
--declare   @age   int
--set  @age=18
--print  @age
--赋值的方式  select
--declare    @Sname  varchar(50)
--select  @Sname=sname  from t_Student   where    SName='王莉莉'
--print @sname
--如果是常量值  用 set   如果是动态值 用select

--declare    @Sgrade     int
--select   @Sgrade=SGrade from   t_Student where    SName='王莉莉'
--print @Sgrade
--select  * from  t_Student  where SGrade>@Sgrade

select  * from t_Student

--declare  @Sname  varchar(50),
--@scode   uniqueidentifier,
--@score   int
--set   @Sname='金蝶'
--select @scode= scode from t_Student where SName=@Sname
--select    @score=Score  from   t_Score  where StudentID=@scode
--print  'Code '+ convert(varchar(50),@scode)
--print 'Score '+ cast(@score as varchar(20))

--declare   @scoreAvg  float 
--select  @scoreAvg=AVG(score) from  t_Score
--print @scoreavg
--if(@scoreAvg>70)
--begin
--   print  '考试成绩优秀'
--   select   top 3   * from t_Score  order by Score desc
--end
--else
--begin
--   print '考试成绩较差'
--   select   top 3   * from t_Score  order by Score  asc
--end


--declare  @count   int
--while(1=1)
--begin
--select  @count=COUNT(studentID) from t_Score  where Score<61
--print @count
--if(@count>0)
--begin
--   update   t_Score   set Score+=2   where Score<61 
--end
--else
--begin
--  break
--end
--end


--declare  @index  int,
--@sum  int=0
--set  @index=0
--while(@index<101)
--begin
--    set @sum=@index+@sum
--	set @index+=1
--end
--print   'SuM '+Cast(@sum as  varchar(50))



select  * from  t_Score

--select  score ,case   
--when Score=100  then    '优秀'
--when Score<100 and  Score>90 then   '良好'
--when Score<91  and Score>80  then    '及格'  
--else   '菜鸡'  end    '中式打分'  
--from  t_Score
--go

--where  条件列 就是子查询的 查询列
--如果子查询用的是 比较运算符 那么一定在子查询的语句中   要加上where
--select  * from  t_Student  
--where  SGrade<(select  SGrade  from t_Student where SName='金蝶 ')

--select  * from  t_Student  
--where  SGrade<2,1,2,2,231,23

--子查询替换表连接    inner   join
--select   * from  t_Student
--inner join    t_Score    on  t_Student.Scode=t_Score.StudentID

--select   * from  t_Student where Scode   in (select  StudentID   from  t_Score)
--select   * from  t_Student where Scode not  in (select  StudentID   from  t_Score)


--if exists (select  * from t_Score  where Score>80  and  Score<100)
--begin
--     update   t_Score   set Score+=2 where Score>80  and  Score<100
--end
--else 
--begin
--   update   t_Score   set Score+=5 where Score<80 
--end





--if   not exists (select  * from t_Score  where Score>80  and  Score<100)
--begin
--     update   t_Score   set Score+=2 where Score>80  and  Score<100
--end
--else 
--begin
--   update   t_Score   set Score+=5 where Score<80 
--end


declare  @i  int=0,@j  int =0 , @z int=0,@g  decimal(10,4)=0
select   @i=COUNT(scode) from t_Student
select @j=COUNT(scode)  from t_Student where scode  in(select   StudentID from t_Score)
set @z=@i-@j
set @g=cast(@j as decimal(10,4))/@i
select  @i '实到人数',@j '应到人数 ',@z '缺考人数',CAST(CAST((@g*100)as int) as varchar(50))+'%'


declare  @avg  int=0
select  @avg=avg(score)  from t_Score
print  @avg
if  exists (select   *  from   t_Score  where Score<@avg)
begin
while(1=1)
begin
   update   t_Score  set   Score+=1 where Score<97
   if not exists(select  * from  t_Score  where Score<97)
   begin
     break
   end
end
end
else
begin
  print '没有低于平均分的人'
end

select  SName,Score,case  
when Score>90 and Score<101 then   '牛逼'
else  '未参加考试' end 
from  t_Student  s
left join   t_Score  c   on s.Scode=c.StudentID






select  * from  t_Score