Today, I figured out how to do a EXCEPT union equivilant in MySQL:
How do you get all of the rows in a table that DON'T exist in another? Here it is folks!
SELECT a.*
FROM big_list a
LEFT JOIN little_list b
ON a.id=b.id
WHERE b.id IS NULL
The 'IS NULL' part is the key. Any row that exists in big_list... that is not in little_list... will return a NULL from the JOIN statement. The WHERE statement looks for the NULL, so all rows not in little_list are returned.
This info comes in handy when, for example, a survey module needs to display a list of questions that are not already in the survey. As an administrator, I would want to see all questions that are not already selected.
