mongodb聚合查询

有个需求是要统计mongodb的数据，按日期查询

如下图，按月查询

db.getCollection('ch_diet').aggregate([
    {
        "$match": {
            "CH_create_time": {"$gt": ISODate("2018-12-31T16:00:00.000Z"), "$lt": ISODate("2019-12-31T16:00:00.000Z")},
            "CH_comment": {"$exists": true},
            "CH_comment.CH_description": {$ne: ""}
        }
    },
    {
        "$project": {
           // 处理时区，因为mongo存储的是UTC时间，加8时区
           day: {$dayOfMonth: {date: "$CH_m_date", timezone: "+08"}},
        }
    },
    {
        "$group": {
             _id: "$day",
            sum: {$sum: 1},

        }
    },
    {
        "$sort": {
                "_id": 1
            }
        }
])

还有这种情况，统计出总数来，还要统计人数多少，就是要根据人的id去重，需要group两次

参考了这篇文章：https://blog.youkuaiyun.com/lff0305/article/details/50034735

db.getCollection('ch_glucose').aggregate([
    {
        "$match": {
            "CH_m_date": {"$gt": ISODate("2020-01-31T16:00:00.000Z"), "$lt": ISODate("2020-02-10T16:00:00.000Z")}
        }
    },
    {
        "$group": {_id: {"date": {$dayOfMonth: {date: "$CH_m_date", timezone: "+08"}}, "user":"$CH_user_id"}}
    },
   {
       "$group": {_id: {"date": "$_id.date"}, count: {$sum: 1}}
    },
    {
        "$sort": {
                "_id": 1
            }
        }
])