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  • Mongo聚合函数

    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d1"), "a" : "张三", "b" : 11, "list": [ { "name" : "aaaa", "age" : 21 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d2"), "a" : "张三1", "b" : 22, "list": [ { "name" : "bbbb", "age" : 123 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d3"), "a" : "张三2", "b" : 33, "list": [ { "name" : "cccc", "age" : 21 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d4"), "a" : "张三3", "b" : 44, "list": [ { "name" : "dddd", "age" : 21 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d5"), "a" : "张三4", "b" : 55, "list": [ { "name" : "eeee", "age" : 21 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d6"), "a" : "张三1", "b" : 66, "list": [ { "name" : "ffff", "age" : 19 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d7"), "a" : "张三2", "b" : 77, "list": [ { "name" : "gggg", "age" : 28 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d8"), "a" : "张三3", "b" : 88, "list": [ { "name" : "hhhh", "age" : 28 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221d9"), "a" : "张三4", "b" : 99, "list": [ { "name" : "mmmm", "age" : 21 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221da"), "a" : "张三", "b" : 11, "list": [ { "name" : "gggg", "age" : 28 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221db"), "a" : "张三", "b" : 22, "list": [ { "name" : "hhhh", "age" : 28 } ] }
    { "_id" : ObjectId("57301c7e5fd5d6e2afa221dc"), "a" : "张三", "b" : 33, "list": [ { "name" : "mmmm", "age" : 21 } ] }

    可以计算出一共有多少条数据

    > db.aa.count()
    12

    count和find一样只有满足条件的才会参与计算

    > db.aa.count({a:"张三"})
    4


    distinct
    db.runCommand({"distinct":[集合名称], "key":[需要区分的字段])

    > db.runCommand({"distinct":"aa","key":"a"})
    {
      "values" : [
          "张三",
          "张三1",
          "张三2",
          "张三3",
          "张三4"
      ],
      "stats" : {
          "n" : 12,
          "nscanned" : 12,
          "nscannedObjects" : 12,
          "timems" : 76,
          "cursor" : "BasicCursor"
      },
      "ok" : 1
    }

    /* 0 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c4"),
      "name" : "张三",
      "books" : [{
          "name" : "mongo权威指南",
          "money" : 44.0,
          "page" : 643.0
        }, {
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }]
    }
    
    /* 1 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c5"),
      "name" : "李四",
      "books" : [{
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }]
    }
    
    /* 2 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c6"),
      "name" : "王二",
      "books" : [{
          "name" : "数学",
          "money" : 28.0,
          "page" : 208.0
        }, {
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }]
    }
    
    /* 3 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c7"),
      "name" : "麻子",
      "books" : [{
          "name" : "英语",
          "money" : 36.0,
          "page" : 102.0
        }, {
          "name" : "化学",
          "money" : 8.0,
          "page" : 77.0
        }]
    }
    
    /* 4 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c8"),
      "name" : "王五",
      "books" : [{
          "name" : "地理",
          "money" : 59.0,
          "page" : 54.0
        }, {
          "name" : "化学",
          "money" : 8.0,
          "page" : 77.0
        }, {
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }]
    }
    
    /* 5 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8c9"),
      "name" : "赵六",
      "books" : [{
          "name" : "生物",
          "money" : 22.0,
          "page" : 66.0
        }, {
          "name" : "化学",
          "money" : 8.0,
          "page" : 77.0
        }, {
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }]
    }
    
    /* 6 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8ca"),
      "name" : "孙七",
      "books" : [{
          "name" : "化学",
          "money" : 8.0,
          "page" : 77.0
        }, {
          "name" : "语文",
          "money" : 200.0,
          "page" : 45.0
        }]
    }
    
    /* 7 */
    {
      "_id" : ObjectId("572ae180734e0336c344e8cb"),
      "name" : "张三",
      "books" : [{
          "name" : "数学",
          "money" : 44.0,
          "page" : 643.0
        }, {
          "name" : "语文",
          "money" : 17.0,
          "page" : 45.0
        }, {
          "name" : "英语",
          "money" : 44.0,
          "page" : 643.0
        }]
    }
    View Code


    db.aa.aggregate({"$project":{"books":1,"_id":0}})
    $project 可以books从每个文档中投影出来。
    这个语法与查询中德字段选择器比较像:可以通过指定 "fieldname":1选择需要投射的字段,或者通过指定"fieldname":0排除不需要的字段。执行完这个操作之后,结果集中的每个文档都会以{"_id":id,"books":"books"}这样的形式表示。


    db.aa.aggregate({"$group":{"_id":"$name","count":{"$sum":1},"aaaa":{"$sum":1}}})
    这里首先指定了需要进行分组的字段 "name"。这是由 "_id":"$name"指定的。
    第二个字的的艺术是为分组内每个文档的 "count" 字段加1.
    count这个字段是我们自己定义的一个字段。

    db.aa.aggregate({"$group":{"_id":"$name","count":{"$sum":1},"aaaa":{"$sum":1}}},{"$sort":{"count":1}})
    {"$sort":{"count":1}}
    这个操作会对结果集中的文档根据count字段进行降序操作。 -1为升序操作


    db.aa.aggregate({"$group":{"_id":"$name","count":{"$sum":1},"aaaa":{"$sum":1}}},{"$limit":2})
    {"$limit":2}
    这个操作会将最终的返回结果集限制为当前结果中的前2个


    db.aa.aggregate({"$group":{"_id":"$name","count":{"$sum":1},"aaaa":{"$sum":1}}},{"$skip":2})
    {"$skip":2}
    接受一个数字n,然后抛弃掉结果集中的前n个文档,将剩余的文档作为结果集返回。


    db.aa.aggregate({"$match":{"name":"张三"}})
    db.aa.aggregate({"$match":{"name":"张三"}},{"$group":{"_id":"$name","count":{"$sum":1},"aaaa":{"$sum":1}}})
    {"$match":{"name":"张三"}}
    $match用于对文档集合进行筛选,之后就可以在筛选得到的文档子集上做聚合。

    db.aa.aggregate({ "$unwind" : "$books" },{"$group":{"_id":{"book":"$books.name","money":"$money"},"count":{"$sum":1}}})
    { "$unwind" : "$books" }
    拆分可以将数组中的每一个值拆分为独立的文档,例如books中是一个集合,使用unwind就可以把这些集合给拉平了,然后再进行聚合

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  • 原文地址:https://www.cnblogs.com/ansheng/p/5470688.html
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