What type of join should be used to ensure that all rows from both tables are returned?

Using a full outer join is the appropriate choice when you want to ensure that all rows from both tables are returned, regardless of whether there is a match between the two. A full outer join combines the results of both left and right outer joins. It returns all records from the left table and all records from the right table, pairing them together where there is a match. If no match exists for a particular row in either table, the result set will still include those rows, filling in with NULLs for the missing sides.

This is especially useful in scenarios where it's important to see all data, such as when conducting comprehensive data analysis, or when working with data sets that may have incomplete or missing relationships.