一个简单的触发器问题

我要用触发器实现每天下班时间不能访问表：
create or replace trigger hospital14_dui
before insert or update or delete on hospital14
declare 
v_time varchar2(20);
begin
v_time:=to_char(sysdate,'hh24:mi:ss');
 if (v_time>17:00:00 or v_time<8:00:00)
 then
 raise_application_error(-2000,'a table can not be modified');
 end if;
end;

结果编译出错，是不是 if (v_time>17:00:00 or v_time<8:00:00)
这句写错了？该怎么改呢？

if (v_time>'17:00:00' or v_time<'8:00:00')

就是这句写错了if (v_time>17:00:00 or v_time<8:00:00)
还有一个地方,错误号码范围不对,自定义错误只能用-20001~-20999之间的数字
create or replace trigger hospital14_dui
before insert or update or delete on hospital14
declare  
v_time varchar2(20);
begin
 v_time:=to_char(sysdate,'hh24:mi:ss');
 if (v_time>'17:00:00' or v_time<'8:00:00')
 then
 raise_application_error(-20001,'a table can not be modified');
 end if;
end;

[code=SQL][/code]create or replace trigger hospital14_dui
before insert or update or delete on hospital14
declare
v_time varchar2(20);
begin
v_time:=to_char(sysdate,'hh24:mi:ss');
 if (v_time>'17:00:00' or v_time<'8:00:00')
 then
 raise_application_error(-2000,'a table can not be modified');
 end if;
end
少了引号。

谢谢，晕啊！好糊涂的我