"As the DBA, your manager called a meeting and asked why there are so many orders for customers that don't exist in the customer table. Upon inspection, you observe that the customer table is joined in a one-to-many relationship with orders.
Write a query that would shows which customers were missing for existing orders. Use a join or a subquery.
Propose a solution to your manager for how to correct the problem. There are several alternatives. Present at least one per post, and explain in detail how this data anomaly could happen. Describe your short- and long-term proposal to correct it.