Re: primary keys

On 13/09/2009, at 2:46 AM, Tom Lane wrote:

> Grant Maxwell <grant.maxwell@maxan.com.au> writes:
>> I don't know why it was done this way but it seems to me that the
>> email addresses are unique, non null and could be used as the primary
>> key. This would make the replication much faster and simpler.
>
>> Does anyone out there think the change (number to email address as
>> primary key) would be a bad idea ?
>
> One thing that's often considered a useful attribute of a primary
> key is
> that it be immutable.  In your application, do users ever change their
> email addresses?  If so, what should happen --- is it okay to treat
> that
> as effectively a new entry?
>
This would be ok. The table keeps a list of email addresses and some
stats on them
users may have multiple addresses but would never alter a specific
record.

> Also, if you have any other tables referencing this one via foreign
> keys, you'd have to have them storing the email address instead of
> the serial number; it'll be bulkier and address updates will be that
> much more expensive.
so text PKs will be less efficient than numeric ?
>
> You can find lots and lots and lots of discussion of this topic if
> you search the archives for talk about natural versus surrogate keys.
>
Good pointer = thanks Tom
>             regards, tom lane