I have two tables from my Magento web-shop 

TABLE 1: All orders in system

TABLE 2: All customers in system

I'm trying to create a list of customers who haven't purchased anything.

Both tables share a "customer ID" column - but how do i define the lookup/relationship?

I've trying changing the TABLE 2 ID column to a lookup column, but since not all ID's are present in the order table, i'm left with many blank rows in the ID column.

Both tables will continuously be update.

Thank you in advance for your help!

Julius