WuLiSenSen

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原测试数据: 

[
    { "_id": ObjectId("59a221054afa291a4e0a974d"), "name": "jack", "age": 16, "sex": "male" },
    { "_id": ObjectId("59a221144afa291a4e0a974e"), "name": "lucy", "age": 16, "sex": "female" },
    { "_id": ObjectId("59a221304afa291a4e0a9750"), "name": "lili", "age": 18, "sex": "female" },
    { "_id": ObjectId("59b0a98bf4eee74a4359353d"), "name": "jack", "age": 16, "sex": "male" },
    { "_id": ObjectId("59e5c25a483b8642c5ac3ded"), "name": "jame", "age": 17, "sex": "unknown" }
]

以 age 和 sex 分组，获取 age, sex, name 字段 

db.a_test.aggregate([
    {
        $group: {
            _id: { age: '$age', sex: '$sex' },
            name: { $first: '$name' },
        },
    },
    {
        $project: {
            _id: false,
            age: '$_id.age',
            sex: '$_id.sex',
            name: '$name',
        },
    },
]);

获取到的数据 

[
    { "age": 17, "sex": "unknown", "name": "jame" },
    { "age": 18, "sex": "female", "name": "lili" },
    { "age": 16, "sex": "female", "name": "lucy" },
    { "age": 16, "sex": "male", "name": "jack" }
]

参考链接https://blog.csdn.net/xiojing825/article/details/78362972

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