Re: Using varchar primary keys. - Mailing list pgsql-general

On Tue, Apr 2, 2013 at 10:34 AM, Joe Van Dyk <joe@tanga.com> wrote:
> On Mon, Apr 1, 2013 at 1:11 PM, Tim Uckun <timuckun@gmail.com> wrote:
>>
>>
>>
>>
>> On Tue, Apr 2, 2013 at 8:35 AM, jesusthefrog <jesusthefrog@gmail.com>
>> wrote:
>>>
>>> On the topic of 'natural' versus 'synthetic' primary keys, I am generally
>>> in the camp that an extra ID field won't cost you too much, and while one
>>> may not need it for a simple table (i.e. id, name) one might add any number
>>> of columns later, and you'll be glad to have it.
>>>
>>
>> Nothing prevents you from adding more columns if you use varchar primary
>> keys.
>>
>>>
>>>
>>> My preferred method is to give every table an ID column of UUID type and
>>> generate a UUID using the uuid-ossp contrib module. This also prevents
>>> someone not familiar with the database design from using an ID somewhere
>>> they should not (as is possible with natural PKs) or treating the ID as an
>>> integer, not an identifier (as is all too common with serial integers).
>>>
>>>
>>
>> This would be a concern if you had multi master writes . As far as I know
>> Postgres does not have a true multi master replication system so all the
>> writes have to happen on one server right?
>>
>> As for UUIDs I use them sometimes but I tend to also use one serial column
>> because when I am communicating with people it makes it so much easier to
>> say "dealer number X" than "dealer number SOME_HUGE_UUID".  I often have to
>> talk to people about the data and UUIDs make it very difficult to
>> communicate with humans.
>
>
> I've been wishing for a smaller uuid type for a while. Say you need to
> assign a Order #. Customers might be referencing the number, so you don't
> want it to be too long. But you don't want Order #'s to be guessable or have
> the characters/digits be transposed accidently.
>
> I've been using a unique text column with a default of random_characters(12)
>
> CREATE OR REPLACE FUNCTION public.random_characters(length integer)
>  RETURNS text
>  LANGUAGE sql
>  STABLE
> AS $function$
> SELECT array_to_string(array((
>       SELECT SUBSTRING('abcdefghjkmnpqrstuvwxyz23456789'
>         FROM mod((random()*31)::int, 31)+1 FOR 1)
>       FROM generate_series(1, $1))),'');
> $function$;
>
> This seems to work ok. I don't allow 1's or l's or 0's or O's, as they can
> easily be mistyped or misread.

This is pseudo random and can be guessed, which is maybe dangerous
depending on circumstance.  For stronger random stream go to
pgcrypto.gen_random_bytes().  Also, now you have to worry about
collisions -- the whole point of uuid is to try and keep you from
having to deal with that.

My historical comments in this debate are noted.  To summarize, I
strongly believe that natural keys are often (but not always) better.

merlin