What is Opponent, when Date is 8 April 1999?
CREATE TABLE "uefa_cup_winners_cup" (
  "date" text,
  "round" text,
  "opponent" text,
  "venue" text,
  "result" text,
  "attendance" real
);
SELECT "opponent" FROM "uefa_cup_winners_cup" WHERE "date"='8 april 1999';