What team lost on 20 August 1989?
CREATE TABLE "nsl_cup_winners" (
  "season" text,
  "cup_final_date" text,
  "winning_team" text,
  "score" text,
  "losing_team" text,
  "cup_final_attendance" text
);
SELECT "losing_team" FROM "nsl_cup_winners" WHERE "cup_final_date"='20 august 1989';