 <pre><code>select * from canonical_list_of_tags where tag not in (select tag from used_tags) </code></pre> <p>At least that works in T-SQL for SQL Server ... </p> <p><strong>Edit:</strong> Assuming that the table <code>canonical_list_of_tags</code> is populated with the result of "<em>Given a collection of user specified tags</em>"</p>