Which ship mode has more "deliver in person" instructions, rail or mail?
ship mode refers to l_shipmode; "deliver in person" instruction refers to l_shipinstruct = 'DELIVER IN PERSON'
SELECT IIF(SUM(IIF(l_shipmode = 'RAIL', 1, 0)) - SUM(IIF(l_shipmode = 'MAIL', 1, 0)), 'RAIL', 'MAIL') AS result FROM lineitem WHERE l_shipinstruct = 'DELIVER IN PERSON'