title: SQL group by - merge groups
body: <p>Is it possible to "merge" 2 groups obtained after a SQL statement that use group by. For example if I have a field size ENUM('extra-small, 'small', 'medium', 'large', extra-large') and then I run this query <code>SELECT * from clothes GROUP BY size;</code>, but for in one case I would like to get in result "extra-small" and "small" in the same group. Is this possible with SQL?</p>