What's the difference between "{CUBE}.id = {orders}.product_id" and "{CUBE}.id = {orders.customer_id}"

FAQs
1

You might sometimes see a join structured:

"{CUBE}.id = {orders}.product_id"

or

"{CUBE}.id = {orders.customer_id}"

Basically everything inside { and } relates to the cubes, whereas everything outside is SQL.
So {orders}.product_id references the product_id column in the database, whereas {orders.customer_id references the customer_id dimension in the orders model.