On What Date is the Competition Semifinal that has a result of 2-1 aet?
CREATE TABLE "matches_and_goals_scored_at_world_cup_an" (
  "match" text,
  "date" text,
  "location" text,
  "lineup" text,
  "result" text,
  "competition" text
);
SELECT "date" FROM "matches_and_goals_scored_at_world_cup_an" WHERE "competition"='semifinal' AND "result"='2-1 aet';