text: -- This on is better than "name text"
  create domain NameValue as varchar(100) not null;
  -- This domain is using for names
  
  create table Drug (
  	-- This one is not good enough
  	-- name text; 
  	name        NameValue,
  	dno         integer,
  	formular    text, -- this can be null
  	primary key (dno)
  );
  
  create table Doctor (
  	name        NameValue,
  	tfn         integer,
  	speciality  text not null,
  	primary key (tfn)
  );
  
  create table Patient (
  	name        NameValue,
  	address     text not null,
  	pid         integer,
  	primary key (pid)
  );
  
  create table Prescribes(
  	"date"      date    not null,
  	quantity    integer not null,
  	drugid      integer references Drug(dno),
  	doctorid    integer references Doctor(tfn),
  	patientid   integer references Patient(pid) not null,
  	primary key ("date", patientid, drugid)
  	-- in the primary key, you do not need doctor because you can go to diff 
  	-- doctor to get the same drug as long as you get the prescribes
  );