Treat

create table Treat(
  Did int references Doctor(Did) on delete cascade,
  Pid int references Patient (Pid) on delete set null,
  Diagnosis varchar(30) not null,
  treat_id int,
  treat_date date
);
insert into Treat values('D_100', 'p_100', 'aaa', 1, '03-11-2000');
insert into Treat values('D_101', 'p_101', 'bbb', 2, '04-11-2010');
insert into Treat values('D_102', 'p_102', 'ccc', 3, '05-11-2009');
insert into Treat values('D_103', 'p_103', 'ddd', 4, '06-11-2005');
insert into Treat values('D_106', 'p_106', 'eee', 5, '07-11-2002');
insert into Treat values('D_104', 'p_104', 'fff', 6, '08-11-2001');