Which date's opponent was Dender when the tournament was in the Jupiler League and the ground was a?
CREATE TABLE "competitive" (
  "date" text,
  "tournament" text,
  "round" text,
  "ground" text,
  "opponent" text,
  "score_1" text
);
SELECT "date" FROM "competitive" WHERE "opponent"='dender' AND "tournament"='jupiler league' AND "ground"='a';