Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_15 (date VARCHAR, motogp_winner VARCHAR, grand_prix VARCHAR)
### Question:
Name the date for motogp winner of casey stoner and grand prix of valencian grand prix
### Answer:
SELECT date FROM table_name_15 WHERE motogp_winner = "casey stoner" AND grand_prix = "valencian grand prix"