1 . Table T1(id: integer not null primary key);
   Table T2(id: integer, idT1: integer references T1 (id) on delete cascade);

 2 . Table T1(id: integer not null primary key);
   Trigger на T1 before delete
     Delete from T2 a where a.id=old.id;

   Table T2(id: integer, idT1: integer);
   Trigger на T2 before insert
     if (not exists (select a.id from T1 a where id=new.id)) then Exception BadRef;
   Trigger на T2 before update
     if (not exists (select a.id from T1 a where id=new.id)) then Exception BadRef;