使用 Mongo 按组计算多个不同的字段

Question

我有一个数据集看起来像

{"BrandId":"a","SessionId":100,"UserName":"tom"}
{"BrandId":"a","SessionId":200,"UserName":"tom"}
{"BrandId":"b","SessionId":300,"UserName":"mike"}

我想按 brandid 计算不同的会话和用户名组，示例 sql 如下：

select brandid,count_distinct(sessionid),count_distinct(username)
from data
group by brandid

我尝试编写 Mongo 数据库，我当前的代码如下，但它不起作用。有没有办法让它发挥作用？

db.logs.aggregate([ 
    {$group:{
        _id:{brand:"$BrandId",user:"$UserName",session:"$SessionId"},  
        count:{$sum:1}}}, 
    {$group:{
        _id:"$_id.brand",
        users:{$sum:"$_id.user"},
        sessions:{$sum:"$_id.session"}
    }}
])

对于特定示例，预期计数为

{"BrandId:"a","countSession":2,"countUser":1}
{"BrandId:"b","countSession":1,"countUser":1}

如果你知道SQL，预期结果与我提到的SQL相同。

Answer 1

您可以使用 $addToSet to accumulate the distinct set of SessionId and UserName values during the $group, and then adding a $project stage to your pipeline that uses the $size 运算符来获取每个集合的大小：

db.logs.aggregate([
    {$group: {
        _id: '$BrandId', 
        sessionIds: {$addToSet: '$SessionId'}, 
        userNames: {$addToSet: '$UserName'}
    }},
    {$project: {
        _id: 0, 
        BrandId: '$_id', 
        countSession: {$size: '$sessionIds'}, 
        countUser: {$size: '$userNames'}
    }}
])

结果：

{
    "BrandId" : "b",
    "countSession" : 1,
    "countUser" : 1
}, 
{
    "BrandId" : "a",
    "countSession" : 2,
    "countUser" : 1
}

使用 Mongo 按组计算多个不同的字段

count multiple distinct fields by group with Mongo

mongodb

aggregation-framework