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Mongodb学习笔记四(Mongodb聚合函数)

2020-01-15 10:25 1116 查看

第四章 Mongodb聚合函数

插入测试数据

for(var j=1;j<3;j++){
for(var i=1;i<3;i++){
var person={
Name:"jack"+i,
Age:i,
Address:["henan","wuhan"],
Course:[
{Name:"shuxue",Score:i},
{Name:"wuli",Score:i}
]
}
db.DemoTest.Person.insert(person)
}
}

Count

db.DemoTest.Person.count({Name:"jack1"})

返回数量

distinct

db.DemoTest.Person.distinct("Name")

返回不重复的Name值。

group

例子：按照Name分组，条件是Age大于46

db.DemoTest.Person.group({
"key":{"Name":true}, -----分组的keky
"initial":{"Person":[]},-------每组分享的一个”初始化函数“
"$reduce":function(cur,prev){   ------这个函数的第一个参数是当前的文档对象，第二个参数是上一次function操作的累计对象，第一次为initial中的{”person“：[]}。有多少个文档， $reduce就会调用多少次

        prev.Person.push(cur);

},
"finalize":function(prev){   ---返回每组的数量
prev.count=prev.Person.length;
},
"condition":{"Age":{"$lt":46}}   -----过滤条件
})

返回结果如下：

/* 0 */
{
"0" : {
"Name" : "jack1",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9d6"),
"Name" : "jack1",
"Age" : 1,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 1
},
{
"Name" : "wuli",
"Score" : 1
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba07"),
"Name" : "jack1",
"Age" : 1,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 1
},
{
"Name" : "wuli",
"Score" : 1
}
]
}
],
"count" : 2
},
"1" : {
"Name" : "jack2",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9d7"),
"Name" : "jack2",
"Age" : 2,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 2
},
{
"Name" : "wuli",
"Score" : 2
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba08"),
"Name" : "jack2",
"Age" : 2,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 2
},
{
"Name" : "wuli",
"Score" : 2
}
]
}
],
"count" : 2
},
"2" : {
"Name" : "jack3",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9d8"),
"Name" : "jack3",
"Age" : 3,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 3
},
{
"Name" : "wuli",
"Score" : 3
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba09"),
"Name" : "jack3",
"Age" : 3,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 3
},
{
"Name" : "wuli",
"Score" : 3
}
]
}
],
"count" : 2
},
"3" : {
"Name" : "jack4",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9d9"),
"Name" : "jack4",
"Age" : 4,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 4
},
{
"Name" : "wuli",
"Score" : 4
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0a"),
"Name" : "jack4",
"Age" : 4,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 4
},
{
"Name" : "wuli",
"Score" : 4
}
]
}
],
"count" : 2
},
"4" : {
"Name" : "jack5",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9da"),
"Name" : "jack5",
"Age" : 5,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 5
},
{
"Name" : "wuli",
"Score" : 5
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0b"),
"Name" : "jack5",
"Age" : 5,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 5
},
{
"Name" : "wuli",
"Score" : 5
}
]
}
],
"count" : 2
},
"5" : {
"Name" : "jack6",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9db"),
"Name" : "jack6",
"Age" : 6,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 6
},
{
"Name" : "wuli",
"Score" : 6
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0c"),
"Name" : "jack6",
"Age" : 6,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 6
},
{
"Name" : "wuli",
"Score" : 6
}
]
}
],
"count" : 2
},
"6" : {
"Name" : "jack7",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9dc"),
"Name" : "jack7",
"Age" : 7,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 7
},
{
"Name" : "wuli",
"Score" : 7
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0d"),
"Name" : "jack7",
"Age" : 7,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 7
},
{
"Name" : "wuli",
"Score" : 7
}
]
}
],
"count" : 2
},
"7" : {
"Name" : "jack8",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9dd"),
"Name" : "jack8",
"Age" : 8,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 8
},
{
"Name" : "wuli",
"Score" : 8
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0e"),
"Name" : "jack8",
"Age" : 8,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 8
},
{
"Name" : "wuli",
"Score" : 8
}
]
}
],
"count" : 2
},
"8" : {
"Name" : "jack9",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9de"),
"Name" : "jack9",
"Age" : 9,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 9
},
{
"Name" : "wuli",
"Score" : 9
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba0f"),
"Name" : "jack9",
"Age" : 9,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 9
},
{
"Name" : "wuli",
"Score" : 9
}
]
}
],
"count" : 2
},
"9" : {
"Name" : "jack10",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9df"),
"Name" : "jack10",
"Age" : 10,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 10
},
{
"Name" : "wuli",
"Score" : 10
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba10"),
"Name" : "jack10",
"Age" : 10,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 10
},
{
"Name" : "wuli",
"Score" : 10
}
]
}
],
"count" : 2
},
"10" : {
"Name" : "jack11",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e0"),
"Name" : "jack11",
"Age" : 11,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 11
},
{
"Name" : "wuli",
"Score" : 11
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba11"),
"Name" : "jack11",
"Age" : 11,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 11
},
{
"Name" : "wuli",
"Score" : 11
}
]
}
],
"count" : 2
},
"11" : {
"Name" : "jack12",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e1"),
"Name" : "jack12",
"Age" : 12,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 12
},
{
"Name" : "wuli",
"Score" : 12
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba12"),
"Name" : "jack12",
"Age" : 12,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 12
},
{
"Name" : "wuli",
"Score" : 12
}
]
}
],
"count" : 2
},
"12" : {
"Name" : "jack13",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e2"),
"Name" : "jack13",
"Age" : 13,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 13
},
{
"Name" : "wuli",
"Score" : 13
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba13"),
"Name" : "jack13",
"Age" : 13,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 13
},
{
"Name" : "wuli",
"Score" : 13
}
]
}
],
"count" : 2
},
"13" : {
"Name" : "jack14",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e3"),
"Name" : "jack14",
"Age" : 14,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 14
},
{
"Name" : "wuli",
"Score" : 14
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba14"),
"Name" : "jack14",
"Age" : 14,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 14
},
{
"Name" : "wuli",
"Score" : 14
}
]
}
],
"count" : 2
},
"14" : {
"Name" : "jack15",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e4"),
"Name" : "jack15",
"Age" : 15,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 15
},
{
"Name" : "wuli",
"Score" : 15
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba15"),
"Name" : "jack15",
"Age" : 15,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 15
},
{
"Name" : "wuli",
"Score" : 15
}
]
}
],
"count" : 2
},
"15" : {
"Name" : "jack16",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e5"),
"Name" : "jack16",
"Age" : 16,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 16
},
{
"Name" : "wuli",
"Score" : 16
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba16"),
"Name" : "jack16",
"Age" : 16,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 16
},
{
"Name" : "wuli",
"Score" : 16
}
]
}
],
"count" : 2
},
"16" : {
"Name" : "jack17",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e6"),
"Name" : "jack17",
"Age" : 17,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 17
},
{
"Name" : "wuli",
"Score" : 17
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba17"),
"Name" : "jack17",
"Age" : 17,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 17
},
{
"Name" : "wuli",
"Score" : 17
}
]
}
],
"count" : 2
},
"17" : {
"Name" : "jack18",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e7"),
"Name" : "jack18",
"Age" : 18,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 18
},
{
"Name" : "wuli",
"Score" : 18
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba18"),
"Name" : "jack18",
"Age" : 18,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 18
},
{
"Name" : "wuli",
"Score" : 18
}
]
}
],
"count" : 2
},
"18" : {
"Name" : "jack19",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e8"),
"Name" : "jack19",
"Age" : 19,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 19
},
{
"Name" : "wuli",
"Score" : 19
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba19"),
"Name" : "jack19",
"Age" : 19,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 19
},
{
"Name" : "wuli",
"Score" : 19
}
]
}
],
"count" : 2
},
"19" : {
"Name" : "jack20",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9e9"),
"Name" : "jack20",
"Age" : 20,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 20
},
{
"Name" : "wuli",
"Score" : 20
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1a"),
"Name" : "jack20",
"Age" : 20,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 20
},
{
"Name" : "wuli",
"Score" : 20
}
]
}
],
"count" : 2
},
"20" : {
"Name" : "jack21",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ea"),
"Name" : "jack21",
"Age" : 21,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 21
},
{
"Name" : "wuli",
"Score" : 21
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1b"),
"Name" : "jack21",
"Age" : 21,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 21
},
{
"Name" : "wuli",
"Score" : 21
}
]
}
],
"count" : 2
},
"21" : {
"Name" : "jack22",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9eb"),
"Name" : "jack22",
"Age" : 22,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 22
},
{
"Name" : "wuli",
"Score" : 22
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1c"),
"Name" : "jack22",
"Age" : 22,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 22
},
{
"Name" : "wuli",
"Score" : 22
}
]
}
],
"count" : 2
},
"22" : {
"Name" : "jack23",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ec"),
"Name" : "jack23",
"Age" : 23,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 23
},
{
"Name" : "wuli",
"Score" : 23
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1d"),
"Name" : "jack23",
"Age" : 23,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 23
},
{
"Name" : "wuli",
"Score" : 23
}
]
}
],
"count" : 2
},
"23" : {
"Name" : "jack24",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ed"),
"Name" : "jack24",
"Age" : 24,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 24
},
{
"Name" : "wuli",
"Score" : 24
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1e"),
"Name" : "jack24",
"Age" : 24,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 24
},
{
"Name" : "wuli",
"Score" : 24
}
]
}
],
"count" : 2
},
"24" : {
"Name" : "jack25",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ee"),
"Name" : "jack25",
"Age" : 25,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 25
},
{
"Name" : "wuli",
"Score" : 25
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba1f"),
"Name" : "jack25",
"Age" : 25,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 25
},
{
"Name" : "wuli",
"Score" : 25
}
]
}
],
"count" : 2
},
"25" : {
"Name" : "jack26",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ef"),
"Name" : "jack26",
"Age" : 26,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 26
},
{
"Name" : "wuli",
"Score" : 26
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba20"),
"Name" : "jack26",
"Age" : 26,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 26
},
{
"Name" : "wuli",
"Score" : 26
}
]
}
],
"count" : 2
},
"26" : {
"Name" : "jack27",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f0"),
"Name" : "jack27",
"Age" : 27,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 27
},
{
"Name" : "wuli",
"Score" : 27
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba21"),
"Name" : "jack27",
"Age" : 27,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 27
},
{
"Name" : "wuli",
"Score" : 27
}
]
}
],
"count" : 2
},
"27" : {
"Name" : "jack28",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f1"),
"Name" : "jack28",
"Age" : 28,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 28
},
{
"Name" : "wuli",
"Score" : 28
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba22"),
"Name" : "jack28",
"Age" : 28,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 28
},
{
"Name" : "wuli",
"Score" : 28
}
]
}
],
"count" : 2
},
"28" : {
"Name" : "jack29",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f2"),
"Name" : "jack29",
"Age" : 29,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 29
},
{
"Name" : "wuli",
"Score" : 29
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba23"),
"Name" : "jack29",
"Age" : 29,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 29
},
{
"Name" : "wuli",
"Score" : 29
}
]
}
],
"count" : 2
},
"29" : {
"Name" : "jack30",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f3"),
"Name" : "jack30",
"Age" : 30,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 30
},
{
"Name" : "wuli",
"Score" : 30
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba24"),
"Name" : "jack30",
"Age" : 30,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 30
},
{
"Name" : "wuli",
"Score" : 30
}
]
}
],
"count" : 2
},
"30" : {
"Name" : "jack31",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f4"),
"Name" : "jack31",
"Age" : 31,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 31
},
{
"Name" : "wuli",
"Score" : 31
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba25"),
"Name" : "jack31",
"Age" : 31,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 31
},
{
"Name" : "wuli",
"Score" : 31
}
]
}
],
"count" : 2
},
"31" : {
"Name" : "jack32",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f5"),
"Name" : "jack32",
"Age" : 32,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 32
},
{
"Name" : "wuli",
"Score" : 32
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba26"),
"Name" : "jack32",
"Age" : 32,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 32
},
{
"Name" : "wuli",
"Score" : 32
}
]
}
],
"count" : 2
},
"32" : {
"Name" : "jack33",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f6"),
"Name" : "jack33",
"Age" : 33,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 33
},
{
"Name" : "wuli",
"Score" : 33
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba27"),
"Name" : "jack33",
"Age" : 33,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 33
},
{
"Name" : "wuli",
"Score" : 33
}
]
}
],
"count" : 2
},
"33" : {
"Name" : "jack34",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f7"),
"Name" : "jack34",
"Age" : 34,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 34
},
{
"Name" : "wuli",
"Score" : 34
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba28"),
"Name" : "jack34",
"Age" : 34,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 34
},
{
"Name" : "wuli",
"Score" : 34
}
]
}
],
"count" : 2
},
"34" : {
"Name" : "jack35",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f8"),
"Name" : "jack35",
"Age" : 35,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 35
},
{
"Name" : "wuli",
"Score" : 35
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba29"),
"Name" : "jack35",
"Age" : 35,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 35
},
{
"Name" : "wuli",
"Score" : 35
}
]
}
],
"count" : 2
},
"35" : {
"Name" : "jack36",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9f9"),
"Name" : "jack36",
"Age" : 36,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 36
},
{
"Name" : "wuli",
"Score" : 36
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2a"),
"Name" : "jack36",
"Age" : 36,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 36
},
{
"Name" : "wuli",
"Score" : 36
}
]
}
],
"count" : 2
},
"36" : {
"Name" : "jack37",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9fa"),
"Name" : "jack37",
"Age" : 37,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 37
},
{
"Name" : "wuli",
"Score" : 37
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2b"),
"Name" : "jack37",
"Age" : 37,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 37
},
{
"Name" : "wuli",
"Score" : 37
}
]
}
],
"count" : 2
},
"37" : {
"Name" : "jack38",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9fb"),
"Name" : "jack38",
"Age" : 38,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 38
},
{
"Name" : "wuli",
"Score" : 38
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2c"),
"Name" : "jack38",
"Age" : 38,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 38
},
{
"Name" : "wuli",
"Score" : 38
}
]
}
],
"count" : 2
},
"38" : {
"Name" : "jack39",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9fc"),
"Name" : "jack39",
"Age" : 39,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 39
},
{
"Name" : "wuli",
"Score" : 39
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2d"),
"Name" : "jack39",
"Age" : 39,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 39
},
{
"Name" : "wuli",
"Score" : 39
}
]
}
],
"count" : 2
},
"39" : {
"Name" : "jack40",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9fd"),
"Name" : "jack40",
"Age" : 40,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 40
},
{
"Name" : "wuli",
"Score" : 40
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2e"),
"Name" : "jack40",
"Age" : 40,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 40
},
{
"Name" : "wuli",
"Score" : 40
}
]
}
],
"count" : 2
},
"40" : {
"Name" : "jack41",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9fe"),
"Name" : "jack41",
"Age" : 41,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 41
},
{
"Name" : "wuli",
"Score" : 41
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba2f"),
"Name" : "jack41",
"Age" : 41,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 41
},
{
"Name" : "wuli",
"Score" : 41
}
]
}
],
"count" : 2
},
"41" : {
"Name" : "jack42",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2b9ff"),
"Name" : "jack42",
"Age" : 42,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 42
},
{
"Name" : "wuli",
"Score" : 42
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba30"),
"Name" : "jack42",
"Age" : 42,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 42
},
{
"Name" : "wuli",
"Score" : 42
}
]
}
],
"count" : 2
},
"42" : {
"Name" : "jack43",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2ba00"),
"Name" : "jack43",
"Age" : 43,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 43
},
{
"Name" : "wuli",
"Score" : 43
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba31"),
"Name" : "jack43",
"Age" : 43,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 43
},
{
"Name" : "wuli",
"Score" : 43
}
]
}
],
"count" : 2
},
"43" : {
"Name" : "jack44",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2ba01"),
"Name" : "jack44",
"Age" : 44,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 44
},
{
"Name" : "wuli",
"Score" : 44
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba32"),
"Name" : "jack44",
"Age" : 44,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 44
},
{
"Name" : "wuli",
"Score" : 44
}
]
}
],
"count" : 2
},
"44" : {
"Name" : "jack45",
"Person" : [
{
"_id" : ObjectId("54461dce69f872cf5ea2ba02"),
"Name" : "jack45",
"Age" : 45,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 45
},
{
"Name" : "wuli",
"Score" : 45
}
]
},
{
"_id" : ObjectId("54461dce69f872cf5ea2ba33"),
"Name" : "jack45",
"Age" : 45,
"Address" : [
"henan",
"wuhan"
],
"Course" : [
{
"Name" : "shuxue",
"Score" : 45
},
{
"Name" : "wuli",
"Score" : 45
}
]
}
],
"count" : 2
}
}

返回的json

mapReduce

mapReduce其实是一种编程模型，用在分布式计算中，其中有一个“map”函数，一个”reduce“函数。

map：

这个称为映射函数，里面会调用emit(key,value)，集合会按照你指定的key进行映射分组。

reduce：

这个称为简化函数，会对map分组后的数据进行分组简化，注意：在reduce(key,value)中的key就是

emit中的key，vlaue为emit分组后的emit(value)的集合，这里也就是很多{"count":1}的数组。

mapReduce:

这个就是最后执行的函数了，参数为map，reduce和一些可选参数。

在MongoDB存储的文档上执行聚合操作非常有用，这种方式的一个限制是聚合函数（比如，SUM、AVG、MIN、MAX）需要通过mapper和reducer函数来定制化实现。

MongoDB没有原生态的用户自定义函数（UDFs）支持。但是它允许使用db.system.js.save命令来创建并保存JavaScript函数，JavaScript函数可以在MapReduce中复用。

第一种统计方式--对应集合直接统计

1.在MongoDB javascript Shell中对Array对象进行了一些扩展，其中新增sum方法，以方便统计数据之用的。

Array.sum=function(arr){
if(arr.length == 0)
return null;
var s = arr[0];
for(var i = 1; i < arr.length; i++)
s += arr[i];
return s;
}

2.例子：按照名称分组，统计每组年龄的和，条件是年龄小于2.

如果统计数量：var map = function(){ emit(this.Name, 1); } 其实是让值永远为1

var map = function(){ emit(this.Name, this.Age); }
var reduce = function( key, values ){ return Array.sum(values); }
var options = {query: { Age: {$lt: 2} }, out: { inline : 1 }}
db.Person.mapReduce(map,reduce,options)

结果如下

/* 0 */
{
"results" : [
{
"_id" : "jack1",
"value" : 2
}
],
"timeMillis" : 0,
"counts" : {
"input" : 2,
"emit" : 2,
"reduce" : 1,
"output" : 1
},
"ok" : 1,
"_o" : {
"results" : [
{
"_id" : "jack1",
"value" : 2
}
],
"timeMillis" : 0,
"counts" : {
"input" : 2,
"emit" : 2,
"reduce" : 1,
"output" : 1
},
"ok" : 1
},
"_keys" : [
"results",
"timeMillis",
"counts",
"ok"
],
"_db" : {
"_mongo" : "connection to localhost:27017{ SSL: { sslSupport: false, sslPEMKeyFile: \"\" } }{ SSH: { host: \"\", port: 22, user: \"\", password: \"\", publicKey: { publicKey: \"\", privateKey: \"\", passphrase: \"\" }, currentMethod: 0 } }",
"_name" : "local",
"system.indexes" : "local.system.indexes",
"prototype" : "local.prototype",
"startup_log" : "local.startup_log",
"TestCollection" : "local.TestCollection",
"TestCollection.Person" : "local.TestCollection.Person",
"DemoTest" : "local.DemoTest",
"DemoTest.Person" : "local.DemoTest.Person",
"system" : "local.system",
"system.js" : "local.system.js",
"mythings" : "local.mythings",
"age_totals" : "local.age_totals",
"Person" : "local.Person"
}
}

结果json

分析一下：
1. map部分
作用：用于分组的。
emit(param1, param2)
param1：需要分组的字段，this.字段名。
param2：需要进行统计的字段，this.字段名。

2. reduce部分
作用：处理需要统计的字段
var reduce = function(key, values){
......统计字段处理
}
key：指分组字段（emit的param1）对应的值
values：指需要统计的字段（emit的param2）值组成的数组

简单介绍统计常用的方法：
* 对数值类型进行求和

var reduce = function(key, values){
return Array.sum(values);
}

* 对字符串类型进行拼凑

var reduce = function(key, values){
return values.join(', ');
}

3. options部分
{ query: { age: {$lt: 25} }, out: "name_totals" }
query：先筛选符合条件的记录出来，再进行分组统计。
out：将分组统计后的结果输出到哪个集合当中。
默认情况下，out所指定的集合在数据库断开连接后再次打开时，依旧存在，并保留之前的所有记录的。

4. 执行分组统计
>db.集合名.mapReduce( map, reduce, options )

第二种统计方式--命令统计

1.命令如下：

注意：out参数 out:"Person_Name" 代表会创建一个临时表Person_Name 然后再从临时表中查找，out:{inline:1} 代表直接显示在当前命令执行的结果中

var map = function(){ emit(this.Name, this.Age); }
var reduce = function( key, values ){ return Array.sum(values); }
db.runCommand({
mapreduce:"Person",
map:map,
reduce:reduce,
out:"Person_Name",
keeptemp: false,
query: { Age:{ $lt: 2 }},
sort:{ Name:1},
    limit:3

})

解析：
mapreduce：
分组统计的集合名
eg：
mapreduce: 'mythings'
不能写成mapreduce: mythings，否则报异常：mythings is not defined

map,reduce ：
同上，不做阐述

out ：
将分组统计结果输出到某个集合。
注意：不能缺省，必须指定名称，否则报错，报错如下：
“exception: 'out' has to be a string or an object”

keeptemp ：
是否保留临时集合（指out指定的集合）
keeptemp：false时会在数据库断开连接后，MongoDB会移除该集合的所有记录。而不是删除。
keeptemp：true时即使数据库断开连接后，再次连接上，该临时集合依旧保持之前所有记录。
keeptemp默认值为true。

query ：
筛选记录后，再进行分组统计
eg:
query: { age:{ $lt: 25 }}

sort ：
对分组统计的集合进行排序，也即先排序，后再执行分组统计的。
注意：这里的排序需要用到索引，必须先创建索引。

limit ：

对分组统计的集合先进行限制返回记录的条数，然后再去进行统计操作。注意：不要理解成对统计后的结果进行限制返回记录条数。

verbose ：
显示时间统计信息，取值为true/false

参考资料

https://www.geek-share.com/detail/2555162000.html

http://www.52ij.com/jishu/3925.html