函的重要功能之一是（ ）。

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SQL Error: select id,body,options from ***_enewstiku where sourceid='29541' and id < 2402622 and id<>'2402622' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='29541' and id > 2402622 and id<>'2402622' order by id asc limit 5