CREATE TABLE table_name_99 (date VARCHAR, opponent_in_the_final VARCHAR, surface VARCHAR)

On what date did the opponent in the Toshiaki Sakai final play on a grass surface?
SELECT date FROM table_name_99 WHERE opponent_in_the_final = "toshiaki sakai" AND surface = "grass"
SELECT "date" FROM "table_name_99" WHERE "grass" = "surface" AND "opponent_in_the_final" = "toshiaki sakai"