Table: tv_ratings_15
Columns: episode_no
airdate
total_viewers
share
bbc_one_weekly_ranking

Question: What were the air-dates of the episodes before episode 4 that had a BBC One weekly ranking of 6?
SQL: SELECT "airdate" FROM tv_ratings_15 WHERE "episode_no" < 4 AND "bbc_one_weekly_ranking" = 6

Question: What was the total viewership for BBC One weekly rankings larger than 7, before episode 4?
SQL: SELECT "total_viewers" FROM tv_ratings_15 WHERE "bbc_one_weekly_ranking" > 7 AND "episode_no" < 4