On Thu, Mar 1, 2018 at 11:32 AM, Daevor The Devoted <dollien@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.
