帮忙解决触发器

ALTER     TRIGGER   INDF   on   个人预订
for   insert
as
if   not   exists(select   1   from   STUDENT..学生   where   学生号   in   (select   学生号   from   inserted))
begin
RAISERROR   ( '该学生号不存在 ',   16,   1)
ROLLBACK   TRANSACTION
end
else  
begin
RAISERROR   ( '该学生号存在 ',   16,   1)
end


exec   insert_indtic   '09105095 '


输出总是该学生号不存在


------解决方案--------------------
抱歉,更正一下:
把:
if not exists(select 1 from STUDENT..学生 where 学生号 in (select 学生号 from inserted))
改成:
if (select count(a.学生号) from STUDENT..学生 as a
inner join inserted as i on a.学生号 = i.学生号) <= 1
--或者:当表中有自动增量标识列时(假设标识列名称为ID)
if not exists(select 1 from STUDENT..学生 as a
inner join inserted as i on a.学生号 = i.学生号 AND a.ID <> i.ID)