alter table t3
add constraint fk_t3 foreign key(sid) references(t1.sid)
on delete cascade
on update cascade
alter table t2
add constraint fk_t2 foreign key(sid) references(t1.sid)
on delete cascade
on update cascade
alter table t3
add constraint fk_t3 foreign key(sid) references(t1.sid)
on delete on update
alter table t2
add constraint fk_t2 foreign key(sid) references(t1.sid)
on delete on update