04. Solutions: FULL OUTER JOIN

Finding Matched and Unmatched Rows with FULL OUTER JOIN

SELECT *
  FROM accounts
 FULL JOIN sales_reps ON accounts.sales_rep_id = sales_reps.id

If unmatched rows existed (they don't for this query), you could isolate them by adding the following line to the end of the query:

WHERE accounts.sales_rep_id IS NULL OR sales_reps.id IS NULL

To elaborate on the rarity of FULL OUTER JOINS in practice, this Stack Overflow answer is helpful: When is a good situation to use a full outer join?