How to make nested list from three table? - php

Question

I have three tables like below:
[Category]->[SubCategory]->[Leaf]
-> means one-to-many relation;
Is it possible to make nested list with just one query?
Actual Query:
Select * from Category
join SubCategory
join Leaf
Intended Output:
Category
--Subcategory
----Leaf
----Leaf
--Subcategory
----Leaf
----Leaf
I know about composite design pattern; but lets say I have the result set from query and I want to manipulate the list above with minimal attempt.
Update
My question is without for loop and sub query, can it be done with the one query above, or what is the best way to generate 3 nested list like above from three tables?
Update:
What is the most optimized way to create a nested list like above from three tables in any database and in any language?

Answer 1

Use this query:
SELECT *
FROM Category c
JOIN SubCategory s ON s.CategoryID = c.ID
JOIN Leaf l ON l.SubCategoryID = s.ID
ORDER BY c.ID, s.ID, l.ID
Then in your PHP loop, print the Category name whenever it changes, print the SubCategory name whenever it changes, and print every Leaf name.
$last_cat = null;
while ($row = fetch()) {
if ($row['CategoryName'] !== $last_cat) {
echo $row['CategoryName'] . "\n";
$last_cat = $row['CategoryName'];
$last_subcat = null;
}
if ($row['SubCategoryName'] != $last_subcat) {
echo "--{$row['SubCategoryName']}\n";
$last_subcat = $row['SubCategoryName'];
}
echo "----{$row['LeafName']\n";
}