mongodb aggregate 求 distinct, count的功能

需求，实现查询，各手游的各渠道的充值人数，充值次数，以及充值总额
select app_id, count(1), count(distinct account_id), sum(recharge_sum) from table group app_id

mongo数据行如下： <!--more-->
&gt; db.t_recharge_history.find({},{"_id":0,"d":0,"s":0});
{ "a" : "121200", "p" : "100037", "c" : "PE", "r" : "12", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 1 }
{ "a" : "121200", "p" : "100037", "c" : "PE", "r" : "1", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 2 }
{ "a" : "332222", "p" : "100037", "c" : "PE", "r" : "3", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 3 }
{ "a" : "333333", "p" : "100062", "c" : "PE", "r" : "123", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 33 }
{ "a" : "333334", "p" : "100062", "c" : "PE", "r" : "44", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 12 }
{ "a" : "333334", "p" : "100062", "c" : "PE", "r" : "44", "rd" : ISODate("2014-08-20T00:00:00Z"), "m" : 1 }
a: 账户
p: 应用id
c: 渠道
r: 角色ID
rd: 充值日期。

查询方法如下：
1. 先作 应用id, 渠道，玩家 的group , 算出每玩家的充值总额，充值次数
db.t_recharge_history.aggregate(
                                                [
                                                  {
                                                    "$match":{
                                                               "rd" : ISODate("2014-08-20T00:00:00Z")
                                                             }
                                                  },
                                                  { "$project": { "p": 1,  "m":1, "a":1, "c":1,"_id":0 }},
                                                  {
                                                      "$group": {
                                                                  "_id": { "app_id" :"$p", "channel_id" : "$c","account_id":"$a" } ,
                                   "cnt": { "$sum": 1},
                                                                  "rmb_sum": { "$sum": "$m"}
                                                                }  
                                                  },
                                                ]
                                            )

的出下面结果。
{
"result" : [
{
"_id" : {
"app_id" : "100037",
"channel_id" : "PE",
"account_id" : "121200"
},
"cnt" : 2,
"rmb_sum" : 3
},

。。。
2. 将1 的结果再次group，按照应用，渠道 作 group
db.t_recharge_history.aggregate(
[
{
"$match":{
"rd" : ISODate("2014-08-20T00:00:00Z")
}
},
{ "$project": { "p": 1, "m":1, "a":1, "c":1,"_id":0 }},
{
"$group": {
"_id": { "app_id" :"$p", "channel_id" : "$c","account_id":"$a" } ,
"cnt": { "$sum": 1},
"rmb_sum": { "$sum": "$m"}
}
},
{
"$group": {
"_id": { "app_id" :"$_id.app_id", "channel_id" : "$_id.app_id" } ,
"player_cnt": { "$sum": 1},
"recharge_items_cnt": { "$sum": "$cnt" },
"rmb_sum": { "$sum": "$rmb_sum"}
}
},
]
)

最终得出结果：
{
"result" : [
{
"_id" : {
"app_id" : "100062"
},
"player_cnt" : 2,
"recharge_items_cnt" : 3,
"rmb_sum" : 46
},
{
"_id" : {
"app_id" : "100037"
},
"player_cnt" : 2,
"recharge_items_cnt" : 3,
"rmb_sum" : 6
}
],
"ok" : 1
}