CREATE TABLE Courses (author_id VARCHAR)
CREATE TABLE Course_Authors_and_Tutors (address_line_1 VARCHAR, author_id VARCHAR)

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
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