GEICO Interview Question

What is the difference between UNION and JOIN in SQL? What is the difference between INNER JOIN and OUTER JOIN in SQL? There was at least one question in the SQL assessment regarding joining 2 tables, and another regarding joining 3 tables. There is a question in the SQL assessment where you have to determine how many rows are resulted from a query that selects from multiple tables WITHOUT using the join function at all. They asked me if I had any customer service experience.