CREATE TABLE table_name_51 (doctor_who_episode VARCHAR, original_airdate__uk_ VARCHAR)

Which Doctor Who episode has a Original airdate (UK) of dvd only?
SELECT doctor_who_episode FROM table_name_51 WHERE original_airdate__uk_ = "dvd only"
SELECT "doctor_who_episode" FROM "table_name_51" WHERE "dvd only" = "original_airdate__uk_"