Re: Simple database design question

I'd bet that you don't call the industry identifier a "sim_id" -- is it a sim_nbr or something?? Ditto for a phone number; I think that is 15 digits in the CITT standard. Learn to use the right names for things, so you can have data interchange, a data dictionary, etc.

CREATE TABLE Sims
(sim_nbr CHAR(n) NOT NULL PRIMARY KEY,

 ..);

CREATE TABLE Phones
(phone_nbr CHAR(15) NOT NULL PRIMARY KEY,
 ..);

Put the sims in the phones ..

CREATE TABLE PhoneSimAssignments
(sim_nbr CHAR(n) NOT NULL UNIQUE -- industry standards?

   REFERENCES Sims(sim_nbr)
   ON DELETE CASCADE,
 phone_nbr CHAR(15) NOT NULL UNIQUE
   REFERENCES Phones(phone_nbr)
   ON DELETE CASCADE,
..);

Use a view to show the sims status of all phones

CREATE VIEW PhoneAssignments (..)
AS
SELECT sim_nbr, phone_nbr, ..
  FROM Phones AS P

       LEFT OUTER JOIN
       PhoneAssignments AS A
       ON A.phone_nbr = P.phone_nbr;