When did the season premiere that had a viewer rank of #6?
CREATE TABLE "ratings" (
  "season" real,
  "season_premiere" text,
  "season_finale" text,
  "tv_season" text,
  "viewer_rank_num" text,
  "households_viewers_in_millions" real
);
SELECT "season_premiere" FROM "ratings" WHERE "viewer_rank_num"='#6';