游标，储存过程，用户定义函数，触发器

此随笔是写给被这些概念困扰的人，你只需复制代码到“查询分析器”逐个调试即可，
同时别忘了在表里添加几条测试用的数据哦。
create table S
(
 S# char(8),
 SNAME varchar(20) not null,
 AGE tinyint,
 SEX bit default 1,
 DNAME char(10),
 primary key(S#),
 check(SEX =0 or SEX = 1)
)

create table C
(
 C# char(8),
 CNAME varchar(8) not null,
 CREDIT tinyint,
 PC# char(8),
 primary key(C#),
 foreign key(PC#) references C(C#)
)

create table SC
(
 S# char(8),
 C# char(8),
 GRADE tinyint,
 primary key (S#,C#),
 foreign key(S#) references S(S#) on delete cascade,
 foreign key(C#) references C(C#) on delete cascade,
 check((GRADE is null) or (GRADE between 0 and 100))
)


游标
     declare @s_id varchar(10),@s_name varchar(20),@message varchar(80),@c_name varchar(20),@sc_grade smallint
print '------------计算机系学生选课情况报表-----------------------'
declare student_cursor cursor for
SELECT S#,SName
FROM S
WHERE DNAME = 'cs'
ORDER BY S#

open student_cursor
fetch next from student_cursor
into @s_id,@s_name
while @@FETCH_STATUS = 0
begin
 print' '
 select @message = @s_name + '学生选修课程:'
 print @message
 --获取当前学生所选修的课程及其成绩
 declare sc_cursor cursor for
 select CNAME,GRADE
 from C,SC
 WHERE C.C# = SC.C# AND SC.S# = @s_id
 
 open sc_cursor 
 fetch next from sc_cursor
 into @c_name,@sc_grade
 if @@FETCH_STATUS <> 0
  print' 该学生没有选课'
 while @@FETCH_STATUS = 0
 begin
  select @message = ' ' + @c_name + ' ' + cast(@sc_grade as varchar)
  print @message
  fetch next from sc_cursor
  into @c_name,@sc_grade
 end
 close sc_cursor
 deallocate sc_cursor
 --获取下一位学生
 fetch next from student_cursor
 into @s_id,@s_name
end
close student_cursor
deallocate student_cursor
go


储存过程
create proc s_c_varg
 @var_grade smallint
as
select SNAME,CNAME,GRADE
from S,C,SC
WHERE S.S# = SC.S#
  AND C.C# = SC.C#
  AND grade > @var_grade

用户定义函数
create function AverageGrade(@dname varchar(20))
returns smallint
begin
 return
 (
  select avg(GRADE)
  from S,SC
  where S.S# = SC.S#
  AND DNAME = @dname
 )
end
go

select S.S#,SNAME
from S,SC
WHERE S.S# = SC.S#
AND   DNAME = 'cs'
AND   GRADE >dbo.AverageGRADE('cs')
GO

触发器
--做一个触发器,当有人试图删除S表中元组时,下面的触发器将向客户端显示一条消息
create trigger reminder
on S
after delete
as
 print '你刚刚删除了一个元组'
go

delete from S where AGE>100