Greetings andrew,

What's your MySQL database schema look like? Is the data example you posted a single table with three columns or just a single column with "|" seperated values stored as a TINYTEXT or similar? That will make a big difference.

Assuming that you have the posted example data in three columns, try this:

SELECT name FROM category WHERE subcat IS NULL OR subcat = ''

More detail: I just finished a project using MySQL where I had a catalog of items. This catalog had categories of items, each category could have sub-categories, and each sub-category could have sub-categories, and so on... Each item in the catalog could be "in" any number of categories or sub-categories or sub-sub-categories.

The way I dealt with it (certainly I'm not claiming this is the best way, of course) was to have a category table with id, name, and parentCategoryId as a foreign key to the same table. That handled all the category stuff because then each sub-category just referenced its parent. The parents with no parents (I called them "elder" categories) simply had NULL for a parentCategoryId. Thus a tree was created.

So to get all the "eldest" categories, I just:

SELECT id, name FROM categories WHERE parentCategoryId IS NULL

Then I just link each item to a category entry with a seperate item/category tables with itemId and categoryId columns.

The real trick (or pain in the butt, depending on your point of view) was starting with a list of items or sub-categories and building the "tree" backwards up to the elder categories. I ended up doing this with a while loop that pushed the categories found into an array.

$sth = $dbh->prepare(q{
  SELECT id, name
  FROM category
  WHERE parentCategoryId = ?
  ORDER BY name
});
my @sub_categories;
my @included_categories = ($root_category_id);
my $included_categories_index = 0;
while ($included_categories_index <= $#included_categories) {
  $sth->execute($included_categories[$included_categories_index]);
  while ($_ = $sth->fetchrow_hashref) {
    push @sub_categories, $_
      if ($included_categories[$included_categories_index] == $root_ca
+tegory_id);
    push @included_categories, $_->{id};
  }
  $included_categories_index++;
}
[download]

I really don't like it; it feels really ungood. However, it's all I could think up at the time.

-gryphon
code('Perl') || die;

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