Find the addresses and author IDs of the course authors that teach at least two courses.
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
addresses and author IDs = SELECT T1.address_line_1, T2.author_id; course authors that teach at least two courses = HAVING COUNT(*) >= 2; joining tables = JOIN ON T1.author_id = T2.author_id;