Message-ID: <48A062EE.5050408@emolecules.com>
Date: Mon, 11 Aug 2008 09:03:58 -0700
From: Craig James <craig_james@emolecules.com>
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To: valiouk@yahoo.co.uk
CC: Jay <arrival123@gmail.com>, pgsql-performance@postgresql.org
Subject: Re: Using PK value as a String
References: <18986.60888.qm@web25807.mail.ukl.yahoo.com>
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Valentin Bogdanov wrote:
> --- On Mon, 11/8/08, Gregory Stark <stark@enterprisedb.com> wrote:
> 
>> From: Gregory Stark <stark@enterprisedb.com>
>> Subject: Re: [PERFORM] Using PK value as a String
>> To: "Jay" <arrival123@gmail.com>
>> Cc: pgsql-performance@postgresql.org
>> Date: Monday, 11 August, 2008, 10:30 AM
>> "Jay" <arrival123@gmail.com> writes:
>>
>>> I have a table named table_Users:
>>>
>>> CREATE TABLE table_Users (
>>>    UserID       character(40)  NOT NULL default
>> '',
>>>    Username   varchar(256)  NOT NULL default
>> '',
>>>    Email          varchar(256) NOT NULL default
>> ''
>>>    etc...
>>> );
>>>
...
>> But the real question here is what's the better design.
>> If you use Username
>> you'll be cursing if you ever want to provide a
>> facility to allow people to
>> change their usernames. You may not want such a facility
>> now but one day...
>>
> 
> I don't understand Gregory's suggestion about the design. I thought
> using natural primary keys as opposed to surrogate ones is a better
> design strategy, even when it comes to performance considerations
> and even more so if there are complex relationships within the database.

No, exactly the opposite.  Data about users (such as name, email address, etc.) are rarely a good choice as a foreign key, and shouldn't be considered "keys" in most circumstances.  As Gregory points out, you're spreading the user's name across the database, effectively denormalizing it.

Instead, you should have a user record, with an arbitrary key, an integer or OID, that you use as the foreign key for all other tables.  That way, when the username changes, only one table will be affected.  And it's much more efficient to use an integer as the key than a long string.

Craig