delete item the order changes php - php

Question

I have a page that has a column "order". When I add a new item the order should be 1 + max of the item. But if I delete an item between these values like i have 8 9 10 , if I delete item with 9 the new item will have 11 value and I will have 8 10 11.But I want 8 9 10. How can I do this in php? should I create a function? It works to add a new item with the max+1, but if I delete is not good.
My code:
$queryMaxOrd = mysql_query("select max(ord) from article where user_id=" .$_SESSION['userId']);
$row = mysql_fetch_row($queryMaxOrd);
$valueMaxOrd = $row[0] + 1;
$_SESSION['a'] = $valueMaxOrd;
and the insert query....
Any ideas?

Answer 1

First thing to consider is removing mysql_* and start using mysqli_* or pdo. Your code is vulnerable to sql injections.
With your code structure you have you adding each order as a new record to your table, so when you have 5 orders with one users your table will look like this.
user: Adiiia | order: 5
user: Adiiia | order: 3
user: Adiiia | order: 7
user: Adiiia | order: 2
user: Adiiia | order: 9
when you query the database you are saying to mysql: get me the maximum number of the record i have with user: Adiiia. The result should be 9
If you want to count the sum of the records you should use sum
select sum(ord) from article where user_id='".$_SESSION['userId']."'
The result should be 26
The best thing you can do is by creating a new table orders_sum
The structure should like like this.
Total_orders | User
when a user have a new order you can update the table by adding one or else if have a order removed then removing minus one order.
Something like this.
Total_orders | User
5 | Adiiia
When you want to update:
select Total_orders from orders_sum where User='Adiiia'
Find how many orders the user have by fetching the table.
$orders = $row['Total_orders'];
$plus_orders = $row['Total_orders'] + 1;
update orders_sum set Total_orders='".$plus_orders."' where user='Adiiia'
When you want to delete:
select Total_orders from orders_sum where User='Adiiia'
Find how many orders the user have by fetching the table.
$orders = $row['Total_orders'];
$minus_orders = $row['Total_orders'] - 1;
update orders_sum set Total_orders='".$minus_orders."' where user='Adiiia'

Answer 2

Lets say article table having primary key article_id then after delete any article for user_id. Fetch all the article_id for the user_id. Then update the order for all the article_id for that user.
$queryArticle = mysql_query("select article_id from article where user_id=" .$_SESSION['userId']." order by article_id asc");
$allArticle = [];
while($rowArticle = mysql_fetch_assoc($queryArticle)){
$allArticle[] = $rowArticle['article_id'];
}
$query = "UPDATE article SET ord = (CASE order ";
foreach($allArticle as $order => $article_id) {
$query .= " WHEN {$article_id} THEN {$order}";
}
$query .= " END CASE) WHERE article_id IN (" . implode(",", $allArticle) . ")";