Question

I am a PHP and MySQL beginner. I am currently doing a top up system that include package service. A customer can purchase available packages which define by admin, table are separate into three: customer, package, customer_package. Customer can slowly spend the package money too so amount are turn into record:

CUSTOMER(ID ......)
PACKAGE(ID , OFFER_RATE , PRICE )
CUSTOMER_PACKAGE( ID, AMOUNT , CUSTOMER_ID, PACKAGE_ID )

I have no problem displaying all choices to the customer, but my problem is if a customer already purchased one of them, how do I only show the rest of the available choices to customer?

My overall idea about the query

SELECT * FROM PACKAGE WHERE ID <>(already in customer_package)

Answer 1

Try a subquery:

SELECT * 
FROM package 
WHERE ID NOT IN (
    SELECT package_id 
    FROM customer_package 
    WHERE customer_id = 55
);

Or a JOIN

SELECT p.* 
FROM package p 
LEFT JOIN customer_package cp ON cp.package_id = p.id AND cp.customer_id = 55 
WHERE cp.id IS NULL

Replace 55 with the proper customer id (variable).