本文描述了MySQL中的常用SQL语句在MongoDB中的写法，如果你长期使用MySQL而对MongoDB跃跃欲试，这篇简单的文章可以帮助你更快的进入角色。

查询：
MySQL:
SELECT * FROM user
Mongo:
db.user.find()

MySQL:
SELECT * FROM user WHERE name = ’starlee’
Mongo:
db.user.find({‘name’ : ’starlee’})

插入：
MySQL:
INSERT INOT user (`name`, `age`) values (’starlee’,25)
Mongo:
db.user.insert({‘name’ : ’starlee’, ‘age’ : 25})

如果你想在MySQL里添加一个字段，你必须：
ALTER TABLE user….
但在MongoDB里你只需要：
db.user.insert({‘name’ : ’starlee’, ‘age’ : 25, ‘email’ : ’starlee@starlee.com’})

删除：
MySQL:
DELETE * FROM user
Mongo:
db.user.remove({})

MySQL:
DELETE FROM user WHERE age < 30
Mongo:
db.user.remove({‘age’ : {$lt : 30}})

$gt : > ; $gte : >= ; $lt : < ; $lte : <= ; $ne : !=

更新:

MySQL:
UPDATE user SET `age` = 36 WHERE `name` = ’starlee’
Mongo:
db.user.update({‘name’ : ’starlee’}, {$set : {‘age’ : 36}})

MySQL:
UPDATE user SET `age` = `age` + 3 WHERE `name` = ’starlee’
Mongo:
db.user.update({‘name’ : ’starlee’}, {$inc : {‘age’ : 3}})

MySQL:
SELECT COUNT(*) FROM user WHERE `name` = ’starlee’
Mongo:
db.user.find({‘name’ : ’starlee’}).count()

MySQL:
SELECT * FROM user limit 10,20
Mongo:
db.user.find().skip(10).limit(20)

MySQL:
SELECT * FROM user WHERE `age` IN (25, 35,45)
Mongo:
db.user.find({‘age’ : {$in : [25, 35, 45]}})

MySQL:
SELECT * FROM user ORDER BY age DESC
Mongo:
db.user.find().sort({‘age’ : -1})

MySQL:
SELECT DISTINCT(name) FROM user WHERE age > 20
Mongo:
db.user.distinct(‘name’, {‘age’: {$lt : 20}})

MySQL:
SELECT name, sum(marks) FROM user GROUP BY name
Mongo:
db.user.group({
key : {‘name’ : true},
cond: {‘name’ : ‘foo’},