which friend of zachs has the longest year relationship?
SELECT T1.name FROM Person AS T1 JOIN PersonFriend AS T2 ON T1.name   =   T2.friend WHERE T2.name  =   'Zach' AND T2.year   =    ( SELECT max ( YEAR )  FROM PersonFriend WHERE name  =   'Zach' ) 
longest year relationship refers to MAX(year); friend of Zach refers to a join condition where T2.name = 'Zach';