按照日期Group的例子

1. Sales表如下：

{"_id":1,"item":"abc","price":10,"quantity":2,"date":ISODate("2014-03-01T08:00:00Z")}{"_id":2,"item":"jkl","price":20,"quantity":1,"date":ISODate("2014-03-01T09:00:00Z")}{"_id":3,"item":"xyz","price":5,"quantity":10,"date":ISODate("2014-03-15T09:00:00Z")}{"_id":4,"item":"xyz","price":5,"quantity":20,"date":ISODate("2014-04-04T11:21:39.736Z")}{"_id":5,"item":"abc","price":10,"quantity":10,"date":ISODate("2014-04-04T21:23:13.331Z")}

2. 按照年月日Group

db.sales.aggregate([{$group:
       {_id:{
                month:{$month:"$date"},
                day:{$dayOfMonth:"$date"},
                year:{$year:"$date"}
        },
        totalPrice:{$sum:{$multiply:["$price","$quantity"]}},
        averageQuantity:{$avg:"$quantity"},
        count:{$sum:1}}
 }])

3. 结果如下

{"_id":{"month":3,"day":15,"year":2014},"totalPrice":50,"averageQuantity":10,"count":1}
{"_id":{"month":4,"day":4,"year":2014},"totalPrice":200,"averageQuantity":15,"count":2}
{"_id":{"month":3,"day":1,"year":2014},"totalPrice":40,"averageQuantity":1.5,"count":2}

官网图

1. MapReduce:

2. Aggregate: