SQL Efficiency Discussion

Folks, I've been pondering a question and I've found it to be more complicated than I initially thought.

Assume we have two very large tables (large enough that discussing efficiency is worthwhile). Let's say one table is named 'course' and the other 'registration', recording the instances of students registering for courses. The goal is simply to filter out the courses that have been registered for by at least one student this year.

It is simple, we can do:

SELECT course.* …

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