Which lots are not used in any transactions? | do you mean the id of lots or the details of lot | The id of the lots please.
SELECT lot_id FROM Lots EXCEPT SELECT T1.lot_id FROM Lots AS T1 JOIN transactions_lots AS T2 ON T1.lot_id   =   T2.lot_id
not used in any transactions refers to lots that do not appear in the transactions_lots table; id of the lots refers to lot_id;