if exists (select *from sysdatabases where name='TRI_school')  
drop database TRI_school  
create database TRI_school  
on primary  
(  
  name='TRI_schoolDB',  
  filename='D:\觸發器\TRI_school.mdf',  
  size=10mb,  
  maxsize=100mb,  
  filegrowth=2mb  
)  




use TRI_school
if exists (select *from sysobjects where name='Student')--學生表  
drop table Student  
create table Student(  
  sno char(10)not null,  
  sname varchar(20)not null,  
  sage smallint,  
  ssex char(1),  
  sdept char(2),  
  xf int default 0,
  jgxf int default 0,
  primary key(sno),  
  check(ssex in ('M','F'))  
) 


if exists (select *from sysobjects where name='Course')--課程表  
drop table Course  
create table Course  
(  
  cno char(10)not null primary key,--定義主鍵  
  cname varchar(20)not null,  
  cpon char(10),  
  credit smallint,  
);  


if exists (select *from sysobjects where name='SC')--選課表  
drop table SC  
create table SC  
(  
sno char(10)not null,  
cno char(10)not null,  
grade smallint ,  
primary key(sno,cno),   
check(grade>=0 and grade<=100)  
)  


create trigger sc_tri on sc
for update,insert,delete
as 
begin
  declare @ycno varchar(10),@ysno varchar(10)
  declare @xcno varchar(10),@xsno varchar(10)
  declare @yxf int ,@xxf int

  select @ycno=cno,@ysno=sno from deleted
  select @xcno=cno,@xsno=sno from inserted
     

   if @xsno is not null--如果現在的學號存在則去學生表中查詢學分是多少
   begin 
   select @xxf=xf from student where 
 
[email protected]
   if @xxf is null--學生表中若沒有學分則置0
   update student set xf=0 where [email protected]
   end    


   if @ysno is not null--//如果原來這個學生就在學生表裡
   begin 
   select @yxf=credit from course where [email protected]查詢原學分
   update student set [email protected] where [email protected]
 
為什麼要刪除？
   end  


  if @xsno is not null
  begin 
  select @xxf=credit from course where [email protected]
  update student set [email protected] where sno [email protected]
  end

end
  --插入操作
insert into student (sno,sname,sage,ssex,sdept)
values('95001','李勇',20,'M','CS');
insert into student (sno,sname,sage,ssex,sdept)
values('95002','劉晨',19,'F','IS');
insert into student (sno,sname,sage,ssex,sdept)
values('95003','王敏',18,'F','MA');
insert into student (sno,sname,sage,ssex,sdept)
values('95004','張立',19,'M','IS');



insert into course(cno,cname,cpon,credit)
values('2','數學',null,2)
insert into course(cno,cname,cpon,credit)
values('6','資料處理',null,2)
insert into course(cno,cname,cpon,credit)
values('7','PASCAL語言','6',4)
insert into course(cno,cname,cpon,credit)
values('4','作業系統','6',3)
insert into course(cno,cname,cpon,credit)
values('5','資料結構','7',4)
insert into course(cno,cname,cpon,credit)
values('1','資料庫','5',4)
insert into course(cno,cname,cpon,credit)
values('3','資訊系統','1',4)


insert into sc values('95001','1',92);
insert into sc values('95001','2',85);
insert into sc values('95001','3',88);
insert into sc values('95002','2',90);
insert into sc values('95002','3',80);
insert into sc values('95003','3',80);



select *from student 
select *from course
select *from sc