MongoDB常用操作
一查询find方法db.collection_name.find()

select * from users;
db.users.find();
指定返回那些列（键）：
select name, skills from users;
db.users.find({}, {'name' : 1, 'skills' : 1});
第一个{} 放where条件 第二个{} 指定那些列显示和不显示 （0表示不显示 1表示显示)

where条件：
1.简单的等于:
select name, age, skills from users where name = 'hurry';
db.users.find({'name' : 'hurry'},{'name' : 1, 'age' : 1, 'skills' : 1});

2.使用and
select name, age, skills from users where name = 'hurry' and age = 18;
db.users.find({'name' : 'hurry', 'age' : 18},{'name' : 1, 'age' : 1, 'skills' : 1});

3.使用or
select name, age, skills from users where name = 'hurry' or age = 18;
db.users.find({ '$or' : [{'name' : 'hurry'}, {'age' : 18}] },{'name' : 1, 'age' : 1, 'skills' : 1});

4.<, <=, >, >= ($lt, $lte, $gt, $gte )
$gt:大于
$lt:小于
$gte:大于或等于
$lte:小于或等于
select * from users where age >= 20 and age <= 30;
db.users.find({'age' : {'$gte' : 20, '$lte' : 30}});

5.使用in, not in ($in, $nin)
select * from users where age in (10, 22, 26);
db.users.find({'age' : {'$in' : [10, 22, 26]}});

6.匹配null
select * from users where age is null;
db.users.find({'age' : null);

7.like (mongoDB 支持正则表达式)
select * from users where name like "%hurry%";
db.users.find({name:/hurry/});
select * from users where name like "hurry%";
db.users.find({name:/^hurry/});

8.使用distinct
select distinct (name) from users;
db.users.distinct('name');

9.使用count
select count(*) from users;
db.users.count();

10.排序
其中 1 为升序排列，而 -1 是用于降序排列。
db.documents.find({}).sort({"created_at":-1});