MongoDB - 如何獲得對活動用戶具有最大正確ansewrs（佔總問題的百分比）的課程

Question

MongoDB - 如何獲得具有活動用戶最大正確ansewrs（佔總問題的百分比）的課程用戶。 有一部分文件。

<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

我覺得你的查詢需要一些改變，因爲它不會ouptut你想要什麼 無需做任何項目的階段，試試這個

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""} 
      } 
      } 
    ]);