CREATE TABLE table_name_79 (episode_number NUMBER, air_date VARCHAR2)

What is the lowest of Episode Number that has a Air Date on 20 july 2007?
SELECT MIN(episode_number) FROM table_name_79 WHERE air_date = "20 july 2007"
SELECT MIN("episode_number") FROM "table_name_79" WHERE "20 july 2007" = "air_date"