SQL doesn't directly support dividing aggregate functions. For example, you can't directly calculate the average order value per customer by dividing the sum of order values by the count of orders. Instead, you need to use subqueries or joins to achieve this. Subqueries are particularly useful for this purpose. They allow you to calculate the necessary intermediate values within a larger query. For instance, you can first calculate the sum of order values and the count of orders for each customer, then divide them in a separate step. Using joins is another approach, but it might not be as efficient as subqueries in some cases. The key is to understand the order of operations and how to correctly nest queries to get the desired result. A crucial consideration is handling potential division by zero errors. If a customer has no orders, the count will be zero, leading to a division by zero error. You need to account for this possibility in your query to prevent errors.