Question

I have the following code

$this->db->query("UPDATE customer_product_owned
   SET quantity = (max(0, (quantity - " . (int)$order_product_upgrade['quantity'] . ")))
   WHERE customer_id = '" . (int)$order_info['customer_id'] . "'");

I would like the php variable to be subtracted from the value of the quantity field. However if the value is less than 0 i want the value to be 0.

What am i doing wrong here? can max be used within a ‘set’? I could do this with an additional query beforehand by first finding out the value of quantity but is there a way to do it in the same query?

Answer 1

1. MAX is an aggregation function. You need GREATEST(0, ...)

2. Don’t enclose numbers in quotes. Just specify them as is, like:

   WHERE customer_id = " . (int)$order_info['customer_id']