What was the product id of the transaction happened at 2012/8/23 21:20:00?
'2012/8/23 21:20:00' can refer to date = '2012-08-23' AND T1.time = '21:20:00' in the database
SELECT T1.ProductID FROM transactions_1k AS T1 INNER JOIN gasstations AS T2 ON T1.GasStationID = T2.GasStationID WHERE T1.Date = '2012-08-23' AND T1.Time = '21:20:00'