user: Question: What is the Serial Number of the Locomotive that Entered Service October 1989?
Columns: ['Locomotive', 'Serial No', 'Entered service', 'Owner', 'Operator', 'Livery', 'Gauge', 'Status']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['G511', '84/1239', 'October 1984', 'Chicago Freight Car Leasing Australia', 'Southern Shorthaul Railroad', 'SSR yellow & black', 'Standard', 'Operational']
SQL:

assistant: SELECT "Serial No" FROM "Table" WHERE "Entered service" = 'October 1989';