CREATE TABLE song (artist_name VARCHAR, f_id VARCHAR)
CREATE TABLE files (f_id VARCHAR, duration VARCHAR)

What is the name of the artist who produced the shortest song?
SELECT T1.artist_name FROM song AS T1 JOIN files AS T2 ON T1.f_id = T2.f_id ORDER BY T2.duration LIMIT 1
SELECT "T1"."artist_name" FROM "song" AS "T1" JOIN "files" AS "T2" ON "T1"."f_id" = "T2"."f_id" ORDER BY "T2"."duration" NULLS FIRST LIMIT 1