user: Question: When was the circuit Portland International Raceway?
Columns: ['Round', 'Race Name', 'Circuit', 'City/Location', 'Date']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, '2006 Imperial Capital Bank Atlantic Race', 'Streets of Long Beach', 'Long Beach, California', 'April 9']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Circuit" = 'Portland International Raceway';