| From: | Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> |
|---|---|
| To: | Greg Smith <greg(at)2ndQuadrant(dot)com> |
| Cc: | Rob Sargent <robjsargent(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: pervasiveness of surrogate (also called synthetic) keys |
| Date: | 2011-05-03 04:53:07 |
| Message-ID: | 4DBF8A33.4080003@postnewspapers.com.au |
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| Thread: | |
| Lists: | pgsql-general |
On 03/05/11 11:07, Greg Smith wrote:
> That doesn't mean you can't use
> them as a sort of foreign key indexing the data; it just means you can't
> make them the sole unique identifier for a particular entity, where that
> entity is a person, company, or part.
Classic case: a database here has several tables indexed by MAC address.
It's used for asset reporting and software inventory.
Problem: VMs generate random MAC addresses by default. They're not
guaranteed to be globally unique. Collisions have happened and will
probably happen again. In this case, it wasn't a big deal, but it just
goes to show that even the "obviously" globally unique isn't necessarily so.
--
Craig Ringer
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