MongoDB-如何為活動用戶獲得具有最大正確答案（占總問題百分比）的課程

Question

MongoDB-如何獲得對活動用戶具有最大正確答案（占總問題百分比）的課程。 文件的一部分。

<code>
     {
    "_id" : 1.0,
    "user_id" : "jjackson0",
    "first_name" : "Jack",
    "last_name" : "Jackson",
    "email" : "jjackson0@apache.org",
    "status" : "active",
    "join_date" : "2014-12-10",
    "last_login_date" : "2016-09-30 23:51:41 -0400",
    "strengths" : [ 
        "mongo queries", 
        "mongo map-reduce queries"
    ],
    "courses" : [ 
        {
            "code" : "CSIS2300",
            "total_questions" : 165.0,
            "correct_answers" : 153.0,
            "incorect_answers" : 12.0
        }
    ]
}

/* 2 */
{
    "_id" : 2.0,
    "user_id" : "ecoleman1",
    "first_name" : "Eugene",
    "last_name" : "Coleman",
    "email" : "ecoleman1@techcrunch.com",
    "age" : 49.0,
    "status" : "banned",
    "join_date" : "2015-07-01",
    "last_login_date" : "2016-09-30 23:54:08 -0400",
    "address" : {
        "city" : "Chencun",
        "province" : "PEI"
    },
    "strengths" : [ 
        "visualization", 
        "sql", 
        "query optimisation", 
        "dimensional modelling", 
        "analytics research"
    ],
    "courses" : [ 
        {
            "code" : "CSIS2300",
            "total_questions" : 188.0,
            "correct_answers" : 106.0,
            "incorect_answers" : 82.0
        }, 
        {
            "code" : "CSIS3300",
            "total_questions" : 12.0,
            "correct_answers" : 9.0,
            "incorect_answers" : 3.0
        }, 
        {
            "code" : "CSIS3380",
            "total_questions" : 172.0,
            "correct_answers" : 142.0,
            "incorect_answers" : 30.0
        }, 
        {
            "code" : "CSIS3360",
            "total_questions" : 140.0,
            "correct_answers" : 21.0,
            "incorect_answers" : 119.0
        }, 
        {
            "code" : "CSIS4260",
            "total_questions" : 163.0,
            "correct_answers" : 75.0,
            "incorect_answers" : 88.0
        }
    ]
}

/* 3 */
{
    "_id" : 3.0,
    "user_id" : "mbowman2",
    "first_name" : "Mark",
    "last_name" : "Bowman",
    "email" : "mbowman2@ebay.co.uk",
    "age" : 36.0,
    "status" : "disabled",
    "join_date" : "2015-02-01",
    "last_login_date" : "2016-09-30 23:58:07 -0400",
    "address" : {
        "city" : "Ban Kruat",
        "province" : "NL"
    },
    "strengths" : [ 
        "mongo map-reduce queries", 
        "sql", 
        "dimensional modelling", 
        "visualization"
    ],
    "courses" : [ 
        {
            "code" : "CSIS2300",
            "total_questions" : 185.0,
            "correct_answers" : 171.0,
            "incorect_answers" : 14.0
        }, 
        {
            "code" : "CSIS3300",
            "total_questions" : 57.0,
            "correct_answers" : 54.0,
            "incorect_answers" : 3.0
        }
    ]
}

/* 4 */
{
    "_id" : 4.0,
    "user_id" : "acollins3",
    "first_name" : "Andrew",
    "last_name" : "Collins",
    "email" : "acollins3@unesco.org",
    "status" : "inactive",
    "join_date" : "2016-03-06",
    "last_login_date" : "2016-09-30 23:59:05 -0400",
    "strengths" : [ 
        "analytics research", 
        "mongo queries", 
        "normalization"
    ],
    "courses" : [ 
        {
            "code" : "CSIS2300",
            "total_questions" : 101.0,
            "correct_answers" : 37.0,
            "incorect_answers" : 64.0
        }
    ]
}

</code>

有我的查詢。 我得到了一些結果，但我想確保它是正確的。

<code>
db.assign1.aggregate([
       {$unwind: "$courses"},
       {$project: 
            {_id: 0,
             user_id: 1,
             max_cor_ans: {$max: "$courses.correct_answers"},
             status: 1,
             course_code: "$courses.code"}
         },
         {$match: {"status": "active"}},
         {$sort: {"max_cor_ans": -1}}
]);
</code>

Answer 1

我認為您的查詢需要一些更改，因為它不會提供您想要的內容，無需執行任何項目階段，請嘗試執行此操作

    db.assign1.aggregate([
           {$match: {"status": "active"}},
           {$unwind: "$courses"},
    {$sort : {"courses.correct_answers" : - 1}}
           { 
             $group: 
                {_id: null,
                 user_id: {$first : "$user_id"},
                 max_cor_ans: {$first: "$courses.correct_answers"},
                 status: {$first : "$status"},
                 course_code: {"$first : "$courses.code""}
             }
          }
    ]);