# An orders table references customers through a customer_id foreign key

Canonical URL: <https://datadriven.io/problems/an-orders-table-references-customers-through-a-customerid-f-67892212>

Domain: Data Modeling · Difficulty: medium

## Problem

An orders table references customers through a customer_id foreign key. Every order must belong to exactly one customer. An employees table references managers through a manager_id foreign key, but the CEO has no manager. Design both tables with the correct nullability on each foreign key.

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