how to update a text field in mysql - php

Question

in my wordpress blog i have a table consist of users and their products seperated by ";" for example :
mytable
----------------------
userid | products
----------------------
1 | camera
2 | books;keyboard;computer
3 | mouse;printer
4 | scanner
now in my script the user will add a new product so i need to check if that user has more than 3 products because in this case i will do nothing and will not add this product for him but if he has less than 3 products i need to add the new product to his products seperated by ";" something like :
$userid = 3;
$newproduct = "ball"
if (pruduct field for that user has more than 2 ";" ) {
do nothing
}else{
$wpdb->update(
'mytable',
array( 'product' => concat(product, ";", $newproduct)),
array( 'userid ' => $userid ),
array( '%s' ),
array( '%d' )
);
so the result in this example would be :
mytable
----------------------
userid | products
----------------------
1 | camera
2 | books;keyboard;computer
3 | mouse;printer;ball
4 | scanner

Answer 1

Despite the data normalization arguments, which are incredibly valid, if for some reason you cannot correct that and must work with what exists.
Select the products column as a string and use the PHP explode() and implode() functions. You'd end up with something like this:
$current_products = explode(';', $user['products']);
// $current_products is now an array of the user's products.
if !(count($current_products) >= 3) {
$current_products[] = $new_product;
}
$user_products = implode(';', $current_products);
// Insert $user_products into your table via UPDATE
The implode and explode functions convert strings to and from arrays based on given delimiters.

Answer 2

In WordPress, the right way to do this is with the user_meta table. With respect, your proposed way is not a good way.
You can set these values into the user_meta table with code like this.
$meta_key = '_my_products'; /* be sure to choose a unique key prefix */
add_user_meta( $userid, $meta_key, 'football', false );
add_user_meta( $userid, $meta_key, 'basketball', false );
You can get them back with code like this
$vals = get_user_meta( $userid, $meta_key, false );
foreach ($vals as $value) {
echo $i;
}
There are other functions for updating and deleting user_meta items. They work well. Read this. https://codex.wordpress.org/Function_Reference/get_user_meta