mongodb 3
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作用SQLmongdb所有记录
SELECT * FROM users
db.users.find()
age=33的记录
SELECT * FROM users WHERE age=33
db.users.find({age:33})
子键（字段）筛选
SELECT a, b FROM users WHERE age=33
db.users.find({age:33}, {a:1,b:1})
排序
SELECT * FROM users WHERE age=33 ORDER BY name
db.users.find({age:33}).sort({name:1})
比大小
SELECT * FROM users WHERE age>33
db.users.find({'age':{$gt:33}})})
正则（模糊匹配）
SELECT * FROM users WHERE name LIKE "Joe%"
db.users.find({name:/^Joe/})
忽略、限制
SELECT * FROM users LIMIT 10 SKIP 20
db.users.find().limit(10).skip(20)
Or操作
SELECT * FROM users WHERE a=1 or b=2
db.users.find( { $or : [ { a : 1 } , { b : 2 } ] } )
仅返回1条(TOP 1)
SELECT * FROM users LIMIT 1
db.users.findOne()
Distinct聚合
SELECT DISTINCT last_name FROM users
db.users.distinct('last_name')
Count聚合
SELECT COUNT(AGE) from users
db.users.find({age: {'$exists': true}}).count()
查询计划
EXPLAIN SELECT * FROM users WHERE z=3
db.users.find({z:3}).explain()
引用自：http://www.mongodb.org/display/DOCS/SQL+to+Mongo+Mapping+Chart
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