id varchar(100),
username varchar(100),
password varchar(100),
isAdmin varchar(1),

CREATE SEQUENCE seq_sys_userlist 
start with 100
increment by 1
MINVALUE 1
MAXVALUE 9999;

create or replace trigger tri_sys_userlist       
before insert on t_sys_userlist       
for each row       
begin       
select 'u'||lpad(seq_sys_userlist.nextval,4,'0') into :new.id from dual;      
end ;  

insert into t_sys_userlist (username,userpassword,isadmin) values('amy','c8837b23ff8aaa8a2dde915473ce0991','0');
commit;

--改成这样子，重新译下，应该就可以了
:new.id := 'u'||lpad(seq_sys_userlist.nextval,4,'0');