MongoDB 使用group by 并显示其他列max值

以下脚本实现功能为把word_info表通过word字段去重，并写到到word_info_new表里

db.word_info.aggregate([
{$group:
        { _id:"$word" ,
         meaning:{$max:"$meaning"}, 
         usphonetic:{$max:"$usphonetic"} 
        }
 }]).forEach(
            function(dc){
                    db.word_info_new.insert(
        {"word":dc._id,
            "meaning":dc.meaning,
            "usphonetic":dc.usphonetic
        }
    )}
    );