Database VS Datastructure

Do u prefer data structures in your scripts? as in Trees, Queues, Stacks .... Do u like arrays? or like classes? Once u get ur data from ur DB would u store it in a Tree for example or would u just take more trips to the database instead? Datascructures make DB so it cant be against it right? Datastructures are live, runtime in ur script while Database is somewhere else that u fetch or play with. So more hits to DB or one hit n playing with ur Trees, Stacks?