Use of User_id

[Stefan Wagner <wa...@ixtern.de>]

Hi!

I got a question regarding the user_id, because I was wondering why it exists 
at all. The login_name is unique already, so why do you create a primary key 
with the user_id? I don't see an advantage.

Thanks for your answers.

Ciao,
Stefan

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Re: Use of User_id

[Scott Eade <se...@backstagetech.com.au>]

From: "Stefan Wagner" <wa...@ixtern.de>
> Hi!
> 
> I got a question regarding the user_id, because I was wondering why it exists 
> at all. The login_name is unique already, so why do you create a primary key 
> with the user_id? I don't see an advantage.
> 
> Thanks for your answers.
> 
> Ciao,
> Stefan

What if you want to change your login_name?  Having user_id insulates you
from having to change values in related tables.

Scott


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Re: Use of User_id

[Jason van Zyl <jv...@apache.org>]

On 8/21/01 6:29 AM, "Stefan Wagner" <wa...@ixtern.de> wrote:

> Hi!
> 
> I got a question regarding the user_id, because I was wondering why it exists
> at all. The login_name is unique already, so why do you create a primary key
> with the user_id? I don't see an advantage.
> 
> Thanks for your answers.

The idea is called a surrogate key, and is explained by Scott Amber in his
papers which you can find at www.ambysoft.com. The unique identifier for an
object should never have any business/domain meaning. A little exerpt from
the Object Primer:

---

Giving your keys meaning is a fatal mistake. If your users decide to change
the business meaning, or if they want to add some digits or make a number
alphanumeric, you need to make changes to your database in every single spot
where you use that information. Anything used as a primary key in one table
is virtually guaranteed to be used in other tables as a foreign key. What
should be a simple change, adding a digit to your customer number, can be a
huge maintenance nightmare. Yuck. In the relational database world, keys
without business meaning are all surrogate keys.

---

He goes into further detail in the book, but the same arguments can be found
in the PDFs that are freely available from Scott Ambler's site.


> Ciao,
> Stefan
> 
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-- 

jvz.

Jason van Zyl

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Re: Use of User_id

[Jon Stevens <jo...@latchkey.com>]

on 8/21/01 3:29 AM, "Stefan Wagner" <wa...@ixtern.de> wrote:

> Hi!
> 
> I got a question regarding the user_id, because I was wondering why it exists
> at all. The login_name is unique already, so why do you create a primary key
> with the user_id? I don't see an advantage.
> 
> Thanks for your answers.
> 
> Ciao,
> Stefan

If you want to join across tables, joining by an integer id is more
efficient than joining with a string.

-jon


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