user: Question: Who is the constructor whose circuit was Oulton Park?
Columns: ['Race Name', 'Circuit', 'Date', 'Winning driver', 'Constructor', 'Report']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Gran Premio Ciudad de Buenos Aires', 'Buenos Aires', '30 January', 'Juan Manuel Fangio', 'Mercedes', 'Report']
SQL:

assistant: SELECT "Constructor" FROM "Table" WHERE "Circuit" = 'Oulton Park';