On Thu, Mar 1, 2018 at 11:32 AM, Daevor The Devoted <doll...@gmail.com> wrote:
> Could you perhaps elaborate on how a surrogate key allows one to insert > garbage into the table? I'm afraid I don't quite get what you're saying. > A bit contrived but it makes the point: *Company:* C1 (id c1) C2 (id c2) *Department:* C1-D1 (id d1) C1-D2 (id d2) C2-D1 (id d3) C2-D2 (id d4) *Employee:* C1-E1 (id e1) C1-E2 (id e2) C2-E1 (id e3) C2-E2 (id e4) *Employee-Department:* e1-d1 e2-d2 e3-d2 e4-d4 The pair e3-d2 is invalid because e3 belongs to company c2 while d2 belongs to company c1 - but we've hidden the knowledge of c# behind the surrogate key and now we can insert garbage into employee-department. David J.
