Context: CREATE TABLE Courses (author_id VARCHAR); CREATE TABLE Course_Authors_and_Tutors (address_line_1 VARCHAR, author_id VARCHAR)
Question: Find the addresses and author IDs of the course authors that teach at least two courses.
Answer: SELECT T1.address_line_1, T2.author_id FROM Course_Authors_and_Tutors AS T1 JOIN Courses AS T2 ON T1.author_id = T2.author_id GROUP BY T2.author_id HAVING COUNT(*) >= 2