在 Oracle Express 中创建触发器

I tried running this, but I don't know how to do it properly.

CREATE TABLE theschema.thetable
(id NUMBER PRIMARY KEY,
name VARCHAR2(30));

CREATE SEQUENCE theschema.test1_sequence
START WITH 1
INCREMENT BY 1;

create or replace trigger insert_nums
before insert on theschema.thetable
for each row
begin
select test1_sequence.nextval into :new.id from dual;
end;
/

当我尝试创建触发器时，会出现一个屏幕，要求我提供一些绑定".该对话框只有一个复选框空".这是什么意思，我该如何制作一个可以正常工作的脚本?