Mysql sub-cat and parent cat with posts [Database schema] - php

Question

Okay so I have a simple category table and a separate posts table easy right but when the user posts a post I wast think should I store both the sub and parent cat in the posts table but would that not be a lot of data duplication so I instead just store the sub_cat then I use a few PHP functions to query the database for the primary cat and its name.
categories table
ID | cat_name | main_cat
1 | Dinner | 0
2 | Chicken | 1
posts table
ID | title | sub_cat | fields that are not related to Q
1 | test | 2 |
Get parent(main) category
$sub_cat = is from a selection query that gets posts and their sub_cats
function main_cat($sub_cat){
require("conn_posts.php");
$stmt = $conn_posts->prepare("SELECT `main_cat` FROM `cats` WHERE `ID` = ?");
$stmt->bind_param("s", $sub_cat);
$stmt->execute();
$stmt_results = $stmt->get_result(); // get result
while($row_get = $stmt_results->fetch_assoc()){
if($row_get['main_cat'] == 0){
return $sub_cat;
}elseif($row_get['main_cat'] !== ""){
return $row_get['main_cat'];
}
}
}
This function gets any category name as long as the id is valid
function cat_name($cat_number){
require("conn_posts.php");
$stmt = $conn_posts->prepare("SELECT `cat_name` FROM `cats` WHERE `ID` = ?");
$stmt->bind_param("s", $cat_number);
$stmt->execute();
$stmt_results = $stmt->get_result(); // get result
$row_get = $stmt_results->fetch_assoc();
if($stmt_results->num_rows <= 0){
return 0;
}elseif($stmt_results->num_rows == 1){
return $row_get['cat_name'];
}
}
My question is is this a good way to process my posts sub-category and parent category are there better ways of doing what I am currently doing? eg. is my database schema good(by good I mean is it better to just include the parent cat id in the posts table than to do the PHP server-side processing)?

Answer 1

Your database schema is good: it doesn't include any replication, I wouldn't change it. The way you're handling fetching the categories in PHP isn't really optimal though: you should almost always aim to minimize the number of queries as it (in general) will affect performance more than the complexity of a query.
If you're running MySQL 8+, a great way to do this is with a recursive CTE; it will allow you to fetch all parents with one query:
WITH RECURSIVE cte AS (
SELECT id, cat_name, main_cat, 0 as depth FROM categories WHERE ID=3
UNION ALL
SELECT categories.id, categories.cat_name, categories.main_cat, cte.depth+1 as depth
FROM cte inner join categories
ON cte.main_cat = categories.id
)
SELECT cat_name FROM cte order by depth ASC
The number '3' in that query can be replaced by the category you're trying to retrieve. You can check this DB fiddle for a live example. If I see your code, incorporating it into your PHP should be fairly trivial. If not, leave a comment and I'll try to expand.