浅谈mongodb中query查询
Mongodb最大的功能之一就是它支持动态查询，就跟传统的关系型数据库查询一样，但是它的查询来的更灵活。
一、 QueryExpressionObjects：查询表达式对象
查询表达式文档也是一个BSON结构的文档，例如，我们可以用下面的查询语句来查询集合中的所有记录：
db.users.find({})
这里，表达式对象是一个空文档，在查询的时候去去匹配所有的记录。再看：
db.users.find({'last_name':'Smith'})
这里，我们将会查询出所有“last_name”属性值为“Smith”的文档记录。
二、查询选项
除了查询表达式意外，Mongodb还支持一些额外的参数选项。例如，我们可能仅仅只想返回某些特定的字段值：
//返回除了age字段外的所有字段
>db.user.find({},{age:0});
//返回tags=tennis除了comments的所有列
db.posts.find({tags:'tennis'},{comments:0});
//返回userid=16的name字段
>db.user.find({userid:16},{name:1});
{"_id":16,"name":"user16"}
//返回x=john的所有z字段
db.things.find({x:"john"},{z:1});
注： _id字段始终都会被返回，哪怕没有明确指定
三、查询条件
1) <,<=,>,>=
//大于:field>value
db.collection.find({"field":{$gt:value}});
//小于：field<value
db.collection.find({"field":{$lt:value}});
//大于等于:field>=value
db.collection.find({"field":{$gte:value}});
//小于等于：field<=value
db.collection.find({"field":{$lte:value}});
2) $all
$all操作类似$in操作，但是不同的是，$all操作要求数组里面的值全部被包含在返回的记录里面，如：
>usetest;
switchedtodbtest
>db.things.insert({a:[1,2,3]});
>db.things.find();
{"_id":ObjectId("4de73360059e7f4bdf907cfe"),"a":[1,2,3]}
>db.things.find({a:{$all:[2,3]}});
{"_id":ObjectId("4de73360059e7f4bdf907cfe"),"a":[1,2,3]}
>db.things.find({a:{$all:[1,2,3]}});
{"_id":ObjectId("4de73360059e7f4bdf907cfe"),"a":[1,2,3]}
>db.things.find({a:{$all:[1]}});
{"_id":ObjectId("4de73360059e7f4bdf907cfe"),"a":[1,2,3]}
>db.things.find({a:{$all:[1,2,3,4]}});
3) $exists
$exists操作检查一个字段是否存在，如：
>for(vari=0;i<1000;i++)db.user.save({_id:i,name:'user'+i,userid:i,age:20});
//包含userid
>db.user.find({userid:{$exists:true}}).limit(5);
{"_id":0,"name":"user0","userid":0,"age":20}
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
//不包含sex字段
>db.user.find({sex:{$exists:false}}).limit(5);
4) $mod
$mod操作可以让我们简单的进行取模操作，而不需要用到where子句，如：
//where子句
>db.user.find("this._id%10==1").limit(5);
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":11,"name":"user11","userid":11,"age":20}
{"_id":21,"name":"user21","userid":21,"age":20}
{"_id":31,"name":"user31","userid":31,"age":20}
{"_id":41,"name":"user41","userid":41,"age":20}
//$mod操作
>db.user.find({_id:{$mod:[10,1]}}).limit(5);
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":11,"name":"user11","userid":11,"age":20}
{"_id":21,"name":"user21","userid":21,"age":20}
{"_id":31,"name":"user31","userid":31,"age":20}
{"_id":41,"name":"user41","userid":41,"age":20}
5) $ne
$ne意思是notequal，不等于，不用多说，看例子：
>db.user.find().limit(5);
{"_id":0,"name":"user0","userid":0,"age":20}
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
>db.user.find({_id:{$ne:0}}).limit(5);
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
{"_id":5,"name":"user5","userid":5,"age":20}
6) $in
$in操作类似于传统关系数据库中的IN，看例子：
//数据库中有所有数组对应的记录
>db.user.find({_id:{$in:[2,3,4,5,6]}}).limit(5);
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
{"_id":5,"name":"user5","userid":5,"age":20}
{"_id":6,"name":"user6","userid":6,"age":20}
//因为数据库中没有_id=1111的记录
>db.user.find({_id:{$in:[2,3,4,5,1111]}}).limit(5);
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
{"_id":5,"name":"user5","userid":5,"age":20}
7) $nin
$nin跟$in操作相反，看例子：
//扣掉_id=1/2/3/4的记录
>db.user.find({_id:{$nin:[1,2,3,4]}}).limit(5);
{"_id":0,"name":"user0","userid":0,"age":20}
{"_id":5,"name":"user5","userid":5,"age":20}
{"_id":6,"name":"user6","userid":6,"age":20}
{"_id":7,"name":"user7","userid":7,"age":20}
{"_id":8,"name":"user8","userid":8,"age":20}
8) $nor、$or
$nor跟$or相反，不好解释，看例子：
>db.user.find({$nor:[{_id:2},{name:'user3'},{userid:4}]}).limit(5);
{"_id":0,"name":"user0","userid":0,"age":20}
{"_id":1,"name":"user1","userid":1,"age":20}
{"_id":5,"name":"user5","userid":5,"age":20}
{"_id":6,"name":"user6","userid":6,"age":20}
{"_id":7,"name":"user7","userid":7,"age":20}
>db.user.find({$or:[{_id:2},{name:'user3'},{userid:4}]}).limit(5);
{"_id":2,"name":"user2","userid":2,"age":20}
{"_id":3,"name":"user3","userid":3,"age":20}
{"_id":4,"name":"user4","userid":4,"age":20}
以上所述就是本文的全部内容了，希望大家能够喜欢。