Optimizing / Simplify Query of Multi-Layer Category - php

Question

I have a MySQL table ( name: item_categories ) having the following schema:
id INT(11) PRIMARY KEY, AUTO INCREMENT
category_name VARCHAR(100) NOT NULL
parent_id INT(11) NOT NULL, Default 0
Sample Data:
id category_name parent_id
=============================
1 Fruit 0
2 Animal 0
3 Furniture 0
4 Apple 1
5 Orange 1
6 Cat 2
7 Dog 2
8 Black Dog 7
9 White Dog 7
If I have to list out the categories with their parent categories, I have to loop through the database table many times.
My question is: How can I simplify the loop task?
Current loop task query:
// 1st query
$sql = "SELECT * FROM item_categories";
$rs = $db->query($sql);
while($row = $db->result($rs)) {
if((int)$row['parent_id'] === 0) {
// it is parent
echo $row['category_name'] . PHP_EOL;
} else {
$category = $row['category_name'];
// it has parent
$sql = "SELECT * FROM item_categories WHERE id=" . $row['parent_id'];
$rs2 = $db->query($sql);
$row2 = $db->result($rs);
$parent_id = (int)$row2['parent_id'];
while($parent_id != 0) {
$sql = "SELECT * FROM item_categories WHERE id=" . $row['parent_id'];
$rs2 = $db->query($sql);
$row2 = $db->result($rs);
$parent_id = (int)$row2['parent_id'];
$category = $row2['category_name'] . ' > ' . $category;
}
echo $category;
}
}
Which will output:
Fruit
Animal
Furniture
Fruit > Apple
Fruit > Orange
Animal > Cat
Animal > Dog
Animal > Dog > Black Dog
Animal > Dog > White Dog

Answer 1

Based on the link i gave you in the comment - try this:
function renderBreadcrumbs($db, $id, $path = null) {
$res = $db->query("SELECT id, parent_id, category_name FROM item_categories WHERE id = " . $id);
$row = $db->result($res);
$path = $row['category_name'] . ' > ' . $path;
if($row['parent_id'])
$path = renderBreadcrumbs($db, $row['parent_id'], $path);
return $path;
}
$res = $db->query("SELECT id, parent_id, category_name FROM item_categories ORDER BY parent_id ASC");
while($row = $db->result($res)) {
$breadcrumb = null;
if(!$row['parent_id'])
$breadcrumb .= $row['category_name'];
else
$breadcrumb .= renderBreadcrumbs($db, $row['parent_id'], $row['category_name']);
echo $breadcrumb . PHP_EOL;
}