products categories - php

Question

I have a simple question but I don't know which term I should use to find the answer (english is not my first language).
I have a classical database design of products like and categories.
CREATE TABLE IF NOT EXISTS `a` (
`id_a` int(11) NOT NULL auto_increment,
`type` varchar(255) NOT NULL,
PRIMARY KEY (`id_a`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=12 ;
CREATE TABLE IF NOT EXISTS `b` (
`id_b` int(11) NOT NULL,
`id_a` int(11) NOT NULL,
`name` varchar(50) NOT NULL,
PRIMARY KEY (`id_b`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
Where b.id_a is a foreign key to a.id_a
I want to get a hierarchy of all thoses like
A VALUE 1
b_value_1
b_value_2
A VALUE 2
b_value_11
b_value_12
A VALUE 3
b_value_21
b_value_22
b_value_23
The request doesn't matters but I get this kind of anwser:
VALUEOF-TABLE-A | VALUEOF-TABLE-B
A VALUE 1 | b_value_1
A VALUE 1 | b_value_2
and so on.
My current code is something like:
$categ = '';
while ($row = mysql_fetch_row ($ressource))
{
if ($row['VALUEOF-TABLE-A']!=$categ)
{
$categ = $row['VALUEOF-TABLE-A'];
echo '<h3>', $categ, '</h3>';
}
echo '<h4>', $row['VALUEOF-TABLE-B'], '</h4>';
}
But I don't like much the idea of the categ variable, be it a string or an id.
Is there an other way to get the data and display them?
Ideally, I'de like a tree object, having only one node for identical children.
Hope you understood what I want.

Answer 1

When working with foreign keys in Mysql, you should use the InnoDB engine instead of MyISAM.
There seems to be a problem in the conception of the b table, id_b should be the primary key, not id_a.
To solve your problem, maybe you should first retrieve the list of id_a, then make one selection request by id_a to select the corresponding id_b using a JOIN.
EDIT : the script should look like this with a little more presentation :
$category_array = mysql_query("SELECT id_a, type FROM a");
while ($category = mysql_fetch_array($category_array))
{
echo $category['type'];
$product_array = mysql_query("SELECT * FROM b WHERE id_a = $id_a");
while ($product = mysql_fetch_array($product_array))
{
echo $product['name'];
}
}

Answer 2

The example Chico gives is on the right track, but has a problem: when there are many categories, the script will also execute many queries, which is inefficient. The following example is much more efficient:
$categories = array();
$category_array = mysql_query("SELECT id_a, type FROM a");
while ($category = mysql_fetch_array($category_array))
{
$category['products'] = array();
$categories[$category['id_a']][] = $category;
}
$product_array = mysql_query("SELECT * FROM b");
while ($product = mysql_fetch_array($product_array))
{
$categories[$product['id_a']]['products'][] = $product
}
foreach($categories as $category) {
echo $category['type'];
foreach ($category['products'] as $product) {
echo $product['name'];
}
}
As an added bonus, this also separates the retrieval of the data more cleanly from the output.