CREATE TABLE table_name_23 (date VARCHAR, surface VARCHAR, score VARCHAR)

What day was the surface clay and the score 6 1, 6 4?
SELECT date FROM table_name_23 WHERE surface = "clay" AND score = "6–1, 6–4"
SELECT "date" FROM "table_name_23" WHERE "6–1, 6–4" = "score" AND "clay" = "surface"