MongoDB 之 aggregate $group 巧妙运用

有这样一组数据：

{ "campaign_id": "A", "campaign_name": "A", "subscriber_id": "123" }, { "campaign_id": "A", "campaign_name": "A", "subscriber_id": "123" }, { "campaign_id": "A", "campaign_name": "A", "subscriber_id": "456" }

按照  campaign_id 与 campaign_name  分组，并查询出每个分组下的记录条数 及  subscriber_id  不同记录的个数

关系型数据库SQL示例：

select campaign_id,campaign_name,count(subscriber_id),count(distinct subscriber_id) group by campaign_id,campaign_name from campaigns;

在MongoDB下就存在两种组合：1） campaign_id, campaign_name, subscriber_id  三个相同的分为一组，

                                                  2） campaign_id, campaign_name  两个相同，subscriber_id 不同分为一组，

最后通过这两种分组查询出按照  campaign_id 与 campaign_name  分组，subscriber_id 不同记录的个数

MongoDB示例：

db.campaigns.aggregate([ { "$match": { "subscriber_id": { "$ne": null }}}, // Count all occurrences { "$group": { "_id": { "campaign_id": "$campaign_id", "campaign_name": "$campaign_name", "subscriber_id": "$subscriber_id" }, "count": { "$sum": 1 } }}, // Sum all occurrences and count distinct { "$group": { "_id": { "campaign_id": "$_id.campaign_id", "campaign_name": "$_id.campaign_name" }, "totalCount": { "$sum": "$count" }, "distinctCount": { "$sum": 1 } }} ])

文档结果：

第一个 group：

{ "_id" : { "campaign_id" : "A", "campaign_name" : "A", "subscriber_id" : "456" }, "count" : 1 } { "_id" : { "campaign_id" : "A", "campaign_name" : "A", "subscriber_id" : "123" }, "count" : 2 }

第二个 group：

{ "_id" : { "campaign_id" : "A", "campaign_name" : "A" }, "totalCount" : 3, "distinctCount" : 2 }

至此，我们已经查询出一共有 3 条记录，subscriber_id 有两种不同的值

reference： Mongodb中Aggregation特性