1.指定返回的键

   db.[documentName].find ({条件},{键指定})

        数据准备persons.json

var persons = [{
 name:"jim",
 age:25,
 email:"75431457@qq.com",
 c:89,m:96,e:87,
 country:"USA",
 books:["JS","C++","EXTJS","MONGODB"]
},
{
 name:"tom",
 age:25,
 email:"214557457@qq.com",
 c:75,m:66,e:97,
 country:"USA",
 books:["PHP","JAVA","EXTJS","C++"]
},
{
 name:"lili",
 age:26,
 email:"344521457@qq.com",
 c:75,m:63,e:97,
 country:"USA",
 books:["JS","JAVA","C#","MONGODB"]
},
{
 name:"zhangsan",
 age:27,
 email:"2145567457@qq.com",
 c:89,m:86,e:67,
 country:"China",
 books:["JS","JAVA","EXTJS","MONGODB"]
},
{
 name:"lisi",
 age:26,
 email:"274521457@qq.com",
 c:53,m:96,e:83,
 country:"China",
 books:["JS","C#","PHP","MONGODB"]
},
{
 name:"wangwu",
 age:27,
 email:"65621457@qq.com",
 c:45,m:65,e:99,
 country:"China",
 books:["JS","JAVA","C++","MONGODB"]
},
{
 name:"zhaoliu",
 age:27,
 email:"214521457@qq.com",
 c:99,m:96,e:97,
 country:"China",
 books:["JS","JAVA","EXTJS","PHP"]
},
{
 name:"piaoyingjun",
 age:26,
 email:"piaoyingjun@uspcat.com",
 c:39,m:54,e:53,
 country:"Korea",
 books:["JS","C#","EXTJS","MONGODB"]
},
{
 name:"lizhenxian",
 age:27,
 email:"lizhenxian@uspcat.com",
 c:35,m:56,e:47,
 country:"Korea",
 books:["JS","JAVA","EXTJS","MONGODB"]
},
{
 name:"lixiaoli",
 age:21,
 email:"lixiaoli@uspcat.com",
 c:36,m:86,e:32,
 country:"Korea",
 books:["JS","JAVA","PHP","MONGODB"]
},
{
 name:"zhangsuying",
 age:22,
 email:"zhangsuying@uspcat.com",
 c:45,m:63,e:77,
 country:"Korea",
 books:["JS","JAVA","C#","MONGODB"]
}]
for(var i = 0;i<persons.length;i++){
 db.persons.insert(persons[i])
}

    1.1 查询出所有数据的指定键(name ,age ,country)

  db.persons.find({},{name:1,age:1,country:1,_id:0})

2.查询条件

2.查询条件

      2.1查询出年龄在25到27岁之间的学生

       db.persons.find({age: {$gte:25,$lte:27},{_id:0,age:1})

      2.2查询出所有不是韩国籍的学生的数学成绩