CREATE TABLE table_42381 ("Date" CLOB, "Tournament" CLOB, "Surface" CLOB, "Opponent" CLOB, "Score" CLOB)

What was the surface for the opponent Roger Federer?
SELECT "Surface" FROM table_42381 WHERE "Opponent" = 'roger federer'
SELECT "Surface" FROM "table_42381" WHERE "Opponent" = 'roger federer'