MongoDB 聚合管道（aggregate）

1、aggregate() 方法

我们先插入一些测试数据

{
    "_id" : ObjectId("5abc960c684781cda6d38027"),
    "name" : "郭大爷",
    "sex" : "男",
    "age" : 80.0,
    "skil" : [
        "PHP",
        "Js",
        "MySql",
        "Html",
        "Css"
    ]
}
{
    "_id" : ObjectId("5abc960c684781cda6d38028"),
    "name" : "郭大爷",
    "sex" : "男",
    "age" : 60.0,
    "skil" : [
        "PHP",
        "MySql"
    ]
}
{
    "_id" : ObjectId("5abc960c684781cda6d38029"),
    "sex" : "女",
    "age" : 15.0,
    "name" : "郭女侠"
}
{
    "_id" : ObjectId("5abc960c684781cda6d3802a"),
    "name" : "郭少爷",
    "sex" : "男",
    "age" : 18.0,
    "skil" : [
        "Css",
        "Java",
        "Html"
    ]
}

• 求和

查询一下所有人年龄的总和

db.userinfo.aggregate([
    { $group : {
        _id : null,
        age_sum : { $sum : "$age" }
    }}
])

结果

{
    "_id" : null,
    "age_sum" : 173.0
}

• 平均值

求所有人年龄的平均值

db.userinfo.aggregate([
    {
        $group:{
            _id: null,
            age_avg: { $avg: "$age" }
        }
    }
]);

结果

{
    "_id" : null,
    "age_avg" : 43.25
}

• 最小值

db.userinfo.aggregate([
    {
        $group: {
            _id: null,
            age_min: { $min: "$age" }
        }
    }
]);

结果

{
    "_id" : null,
    "age_min" : 18.0
}