Which Opponent has a Type of tko, and a Round of 2 (6) on 2006-09-20?
CREATE TABLE "professional_record" (
  "result" text,
  "opponent" text,
  "type" text,
  "round" text,
  "date" text
);
SELECT "opponent" FROM "professional_record" WHERE "type"='tko' AND "round"='2 (6)' AND "date"='2006-09-20';