CREATE TABLE "round_15" (
  "home_team" text,
  "home_team_score" text,
  "away_team" text,
  "away_team_score" text,
  "venue" text,
  "crowd" real,
  "date" text
);

Question: Who was Melbourne's home team opponent?
SQL: SELECT "home_team" FROM "round_15" WHERE "away_team"='melbourne';

Question: Who was Richmond's away team opponent?
SQL: SELECT "away_team" FROM "round_15" WHERE "home_team"='richmond';