CREATE TABLE "round_of_sixteen" (
  "team_1" text,
  "agg" text,
  "team_2" text,
  "1st_leg" text,
  "2nd_leg" text
);

Question: What was the 1st leg of the match that had an aggregate of 4-3?
SQL: SELECT "1st_leg" FROM "round_of_sixteen" WHERE "agg"='4-3';

Question: What was the 2nd leg fo the match that had a 1st leg of 1-3 and aggregate of 1-6?
SQL: SELECT "2nd_leg" FROM "round_of_sixteen" WHERE "1st_leg"='1-3' AND "agg"='1-6';