触发器怎么写

create or replace trigger dml_a
before insert or delete on a
for each row
as
begin
when inserting then
insert into b values(a.:new.字段1,a.:new.字段2...);
when deletint then
delete from b where b.字段=a.:old.字段;
end dml_a;

用约束写行吗？好久没用，如果今天你没满意答案，我晚上回家再看看，明天给你答案
create trigger adddec
before insert or delete on a
for each row
as
begin
when inserting then
你要执行的插入sql语句
when deletint then
你要执行的s删除ql语句
end dml_a;

用delete和update触发器