CREATE TABLE "singles_13_7_6" (
  "date" text,
  "tournament" text,
  "surface" text,
  "opponent" text,
  "score" text
);

Question: What was the surface for October 10, 2004?
SQL: SELECT "surface" FROM "singles_13_7_6" WHERE "date"='october 10, 2004';

Question: What was the surface for the opponent Roger Federer?
SQL: SELECT "surface" FROM "singles_13_7_6" WHERE "opponent"='roger federer';