user: Question: What is the purse when Aidan O'Brien was the trainer?
Columns: ['Year', 'Winner', 'Jockey', 'Trainer', 'Owner', 'Time', 'Purse']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [2013.0, 'London Bridge', 'Mike Smith', 'Jo Hughes', 'Eastwind Racing & Martha Trussell', '2:58.32', '$500,000']
SQL:

assistant: SELECT "Purse" FROM "Table" WHERE "Trainer" = 'Aidan O''Brien';