trigger for update

When using "ON DELETE CASCADE " data in child tables automatically removed when parent table gets deteted

How to write trigger for update .I has follwed as for deleting cascade




create table n1(no number,name varchar2(10),constraint n_k primary key(no));

create table n2 (loc varchar2(10),no references n1(no) on delete cascade);


SQL> select * from n2;

LOC NO
---------- ----------
delhi 1

SQL> select * from n1;

NO NAME
---------- ----------
1 mmm
2 nnn
3 xxx



SQL> delete n1 where no=1;

1 row deleted.

SQL> select * from n2;

no rows selected


Thanks in advance
mohan