CREATE TABLE staff (last_name VARCHAR, staff_id VARCHAR)
CREATE TABLE complaints (staff_id VARCHAR, date_complaint_raised VARCHAR)

What is the last name of the staff who has handled the first ever complaint?
SELECT t1.last_name FROM staff AS t1 JOIN complaints AS t2 ON t1.staff_id = t2.staff_id ORDER BY t2.date_complaint_raised LIMIT 1
SELECT "t1"."last_name" FROM "staff" AS "t1" JOIN "complaints" AS "t2" ON "t1"."staff_id" = "t2"."staff_id" ORDER BY "t2"."date_complaint_raised" NULLS FIRST LIMIT 1