What was the 1st leg of the match that had an aggregate of 4-3?
CREATE TABLE "round_of_sixteen" (
  "team_1" text,
  "agg" text,
  "team_2" text,
  "1st_leg" text,
  "2nd_leg" text
);
SELECT "1st_leg" FROM "round_of_sixteen" WHERE "agg"='4-3';