I want to select from two tables. Each table has a column called "course_id". I want to select from one table if the "course_id" doesn't exist in the other table. How would I do this in one or multiple queries? I was looking at unions, joins, subqueries but I don't know if that is the most efficient or easiest solution. I've messed with all three but with no luck. Any help is appreciated. I'm only really selecting from the first table, but making sure that the "course_id" doesn't exist in the second table.