CREATE TABLE table_2815 ("Outcome" TEXT, "Year" FLOAT, "Championship" TEXT, "Surface" TEXT, "Partner" TEXT, "Opponents" TEXT, "Score" TEXT)

What was the surface during wimbledon in 1974?
SELECT "Surface" FROM table_2815 WHERE "Championship" = 'Wimbledon' AND "Year" = '1974'
SELECT "Surface" FROM "table_2815" WHERE "Championship" = 'Wimbledon' AND "Year" = '1974'