How to change rows in a relational database?

Question

MySQL

Good evening!
There are 3 tables, namely:
STORAGE with id and count fields,
combinations with storage_id, product_id,count fields
AND products with id
field Combinations.count must be subtracted from the storage.count field, for all rows with storage.id = storage_id and product_id = product.id
In this case, the selection goes by products.id with the following query:

UPDATE `storage`
LEFT JOIN `combinations` ON `combinations`.`storage_id` = `storage`.`id`
LEFT JOIN `products` ON `products`.`id` = `combinations`.`product_id`
SET `storage`.`count` = `storage`.`count` - `combinations`.`count`
WHERE `products`.`id` IN (?ai)

Everything works for single subtractions, but there are situations when for one `products`.`id` you need to make a multiple of N number of subtractions.
How to remake a request?

Answer 1

In general, a dangerous approach, because the script can "accidentally" work more than the required number of times and you will have all the values ​​broken. I never do that. I load the values ​​and do all the calculations in the script, so the values ​​remain unchanged.
In general, it is not a very healthy practice to change data in this way. IMHO.