Re: Enforce primary key on every table during dev?

On Thu, Mar 1, 2018 at 11:32 AM, Daevor The Devoted <dollien(at)gmail(dot)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.