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_21 (purse VARCHAR, trainer VARCHAR)
### Question:
What was the purse when the trainer was Aidan O'Brien?
### Answer:
SELECT purse FROM table_name_21 WHERE trainer = "aidan o'brien"