From: Peter Brawley
Date: August 24 2005 4:23am
Subject: Re: Treating Two Fields Like One
List-Archive: http://lists.mysql.com/mysql/188210
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David,

 >1. Some species names are shared by more than one
 >mammal. For example, there's a marsupial named
 >Antechinus leo.

 >2. Species are more properly cited with the name of
 >their parent (genus), so I eventually want my species
 >URL's to look like this:

<snip>

As you note, the names aren't guaranteed to be unique, or to stay the 
same either, therefore they won't do as primary keys, therefore they 
won't do as foreign keys. Also our understanding of these taxonomic 
relationships can change even when the names don't, and it's considered 
a design error to make it necessary to edit primary keys in order to 
update database tables.

One way out is to give every table an auto-incrementing integer PK, and 
use those keys, which will never change, to mark parent-child 
relationships.

It is indeed confusing to try to work out user interface and database 
design issues at the same time. The usual suggestion is to solve the 
database structure problem before you lay a hand on the UI problem. The 
idea is to write a query or query template for every question yoiur 
system may ever be asked, and build the tables that those queries need.

PB


David Blomstrom wrote:

>I'm trying to make my first content management system
>and am wrestling with a problem that seems to be about
>equal parts PHP, Apache mod_rewrite and MySQL. I
>wondered if anyone on this list can suggest a MySQL
>solution - or partial solution.
>
>I'm dealing with a single database table named
>gzanimals that lists animal taxons (orders, families,
>species, etc.) in a child-parent relationship (with
>fields named "Name" and "Parent". For example:
>
>NAME | PARENT
>Animalia | (NULL)
>Mammalia | Animalia
>Carnivora | Mammalia
>Felidae | Carnivora
>Panthera | Felidae
>leo | Panthera
>
>The code above illustrates the taxonomic hierarchy
>linking the lion (Panthera leo) to the animal kingdom
>(Animalia). With Apache mod_rewrite, my URL's look
>like this:
>
>www.geozoo.org/stacks/Animalia
>www.geozoo.org/stacks/Mammalia
>www.geozoo.org/stacks/Carnivora
>www.geozoo.org/stacks/Felidae
>www.geozoo.org/stacks/Panthera
>www.geozoo.org/stacks/leo
>
>There are two problems with this strategy:
>
>1. Some species names are shared by more than one
>mammal. For example, there's a marsupial named
>Antechinus leo.
>
>2. Species are more properly cited with the name of
>their parent (genus), so I eventually want my species
>URL's to look like this:
>
>www.geozoo.org/stacks/Panthera_leo
>
>* * * * *
>
>I can manipulate my PHP script and mod_rewrite to draw
>from two fields and display Panthera_leo instead of
>leo.
>
>The problem is that I more or less lose contact with
>my database; it recognizes leo as a row identifier,
>while Panthera_leo is an unknown.
>
>* * * * *
>
>You can see a good example of what I'm trying to do at
>http://www.geozoo.org/stacks/Carnivora Two separate
>scripts drive the bread crumbs-style links at the top
>of the page and the list of "children" (carnivore
>families, in this case) in the column on the right.
>
>If you click Felidae, the children change to a list of
>genera that belong to the family Felidae. Click
>Panthera - http://www.geozoo.org/stacks/Panthera - and
>the children change to species that belong to the
>genus Panthera.
>
>As you can see, I've modified these so they display
>the genus (parent) + species (child) name, both
>physically and in the link. However, they are
>nonfunctioning, as I haven't yet figured out how to to
>deal with the space between the two values.
>
>* * * * *
>
>At this point, I'm thoroughly confused, especially
>since fixes often require tweakingn two or more things
>simultaneously - PHP, mod_rewrite and MySQL. But one
>thing I haven't experimented with yet is combined
>fields.
>
>I created a key on two fields - Name and Parent - and
>it NameDual. Is there a way to connect with NameDual
>in a PHP script, or is it something that only exists
>in my database?
>
>For example, I thought I might change...
>
>$taxon = mysql_query ("SELECT Name, NameCommon, Parent
>FROM gzanimals AS GZA
> WHERE Parent = '$_GET[taxon]'");
>
>to...
>
>$taxon = mysql_query ("SELECT NameDual, Name,
>NameCommon, Parent FROM gzanimals AS GZA
> WHERE Parent = '$_GET[taxon]'");
>
>...except it didn't work.
>
>Is there a way to do this, or can you see any other
>MySQL solutions to my problem?
>
>Thanks. 
>
>
>
>		
>____________________________________________________
>Start your day with Yahoo! - make it your home page 
>http://www.yahoo.com/r/hs 
> 
>
>  
>


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