>db.t2.aggregate([ { $group: {"_id": { "country" : "$country", "province": "$province" , "uid" : "$userid" } } } ,
{ $group: {"_id": { "country" : "$_id.country", "province": "$_id.province" }, count: { $sum : 1 } } },
{ $project : {"_id": 0, "country" : "$_id.country", "province" : "$_id.province", "count" : 1}}
])
主要是分组统计这块的几个参数