Re: PostgreSQL Developer Best Practices

On 8/25/2015 1:38 PM, Joshua D. Drake wrote:
> But a VIN is in fact, UNIQUE so it is useful as a PK.
>
> JD
>
But a VIN is *not* guaranteed to exist, nor is it guaranteed never to 
change, and I regard those as pretty important characteristics in a PK.

VINs were not required in the U.S. until 1954, and were not in a 
standardized format until 1981; other countries have different dates. If 
you are dealing with [or ever might deal with] pre-war classics, early 
imports, kit cars, or other out-of-the-mainstream vehicles, you have to 
deal with the possibility of a vehicle that doesn't have a traditional 
VIN, certainly not one in the 'expected' 17-character  format. Changing 
VINs likewise are very very rare but not impossible (perhaps the most 
common instance would be something like an antique where they used the 
engine serial number as the VIN, only now it has had the engine replaced 
and the DMV insists it have a new number). A lot of "natural" PKs have 
similar oddities and corner cases that 99.99% of us will never 
encounter, but you don't want to be in the 0.01%. Artificial keys don't 
suffer these problems.

--christine desmuke