At my work, I've been asked to teach a short half-hour to an hour course about "select and joins". I'm also thinking about discussing unions, sub queries and temp tables in this course. Are there any core concepts that relate to the topic of "select and joins" that I could include to expand the length of said course?
In addition to what Brent suggested, I would encourage your staff to look over Aaron Bertrand's list of T-SQL bad habits.
If you only have half an hour and "Select" is actually part of the request, I have to assume you are teaching people brand new to SQL.
I'd be very surprised if you can get past Select Col1 from MyTable, and then move to Joins (innner, left right, etc.).
If they are beginners, this should be example heavy and you should already have your tables for the demo created.
Hope this helps