mongoDB第五讲

CountDistinctGroup 1.Count 请查询persons中美国学生的人数. db.persons.find({country:USA}).count() 2.Distinct 请查询出persons中一共有多少个国家分别是什么. db.runCommand({distinct:persons“, key:country}).values 3.Group 语法: db.runCommand({g

Count+Distinct+Group

1.Count

请查询persons中美国学生的人数.

db.persons.find({country:"USA"}).count()

2.Distinct

请查询出persons中一共有多少个国家分别是什么.

db.runCommand({distinct:"persons“, key:"country"}).values

3.Group

语法:

db.runCommand({group:{

ns:集合名字,

Key:分组的键对象,

Initial:初始化累加器,

$reduce:组分解器,

Condition:条件,

Finalize:组完成器

}})

分组首先会按照key进行分组,每组的 每一个文档全要执行$reduce的方法,

他接收2个参数一个是组内本条记录,一个是累加器数据.

3.1请查出persons中每个国家学生数学成绩最好的学生信息(必须在90以上)

db.runCommand({group:{

ns:"persons",

key:{"country":true},

initial:{m:0},

$reduce:function(doc,prev){

if(doc.m > prev.m){

prev.m = doc.m;

prev.name = doc.name;

prev.country = doc.country;

}

},

condition:{m:{$gt:90}}

}})

3.2在3.1要求基础之上把每个人的信息链接起来写一个描述赋值到m上

finalize:function(prev){

prev.m = prev.name+" Math scores "+prev.m

}

4.用函数格式化分组的键

4.1如果集合中出现键Counrty和counTry同时存在

db.persons.insert({
name:"USPCAT",
age:27,
email:"2145567457@qq.com",
c:89,m:100,e:67,
counTry:"China",
books:["JS","JAVA","EXTJS","MONGODB"]
})

那分组有点麻烦这要如何解决呢?

db.runCommand({group:{
ns:"persons",
$keyf:function(doc){
if(doc.counTry){
return {country:doc.counTry}
}else{
return {country:doc.country}
}
},
initial:{m:0},
$reduce:function(doc,prev){
if(doc.m > prev.m){
prev.m = doc.m;
prev.name = doc.name;
if(doc.country){
prev.country = doc.country;
}else{
prev.country = doc.counTry;
}
}
},
finalize:function(prev){
prev.m = prev.name+" Math scores "+prev.m
},
condition:{m:{$gt:90}}
}})

数据库命令操作

1.命令执行器runCommand

1.1用命令执行完成一次删除表的操作

db.runCommand({drop:"map"})

{

"nIndexesWas" : 2,

"msg" : "indexes dropped forcollection",

"ns" : "foobar.map",

"ok" : 1

}

2.如何查询mongoDB为我们提供的命令

1.在shell中执行 db.listCommands()

2.访问网址http://localhost:28017/_commands，需要先通过

mongod --dbpath d:\app\mongodata --rest命令打开简单的rest API

3.常用命令举例

3.1查询服务器版本号和主机操作系统

db.runCommand({buildInfo:1})

3.2查询执行集合的详细信息,大小,空间,索引等……

db.runCommand({collStats:"persons"})

3.3查看操作本集合最后一次错误信息

db.runCommand({getLastError:"persons"})

固定集合特性

2.固定特性

2.1固定集合默认是没有索引的就算是_id也是没有索引的

2.2由于不需分配新的空间他的插入速度是非常快的

2.3固定集合的顺是确定的导致查询速度是非常快的

2.4最适合的是应用就是日志管理喎?http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">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"a.txt'

服务器端脚本

1.Eval

1.1服务器端运行eval

db.eval("function(name){return name}","uspcat")

2.Javascript的存储

2.1在服务上保存js变量活着函数共全局调用

1.把变量加载到特殊集合system.js中

db.system.js.insert({_id:name,value:”uspcat”})

2.调用

db.eval("return name;")

System.js相当于Oracle中的存储过程,因为value不单单可以写变量

还可以写函数体也就是javascript代码