mongo-aggregate

aggregate group

前提:这是一个对答题积分的统计,diff表示题目难度,diff取值为[0,4]
难度高的题目,得到的积分会更高

db.answers.aggregate([    {$match:{isPass:true}},    {$group:{        _id:{username:'$username',diff:'$diff'},         count:{$sum:{$multiply:[3,{$add:['$diff',1]}]}}    }}]);