MongoDB语法            MySql语法

db.test.find({'name':'foobar'})             <==>          select * from test where name='foobar'

db.test.find()                                       <==>          select *from test

db.test.find({'ID':10}).count()              <==>          select count(*) from test where ID=10

db.test.find().skip(10).limit(20)           <==>          select * from test limit 10,20

db.test.find({'ID':{$in:[25,35,45]}})      <==>          select * from test where ID in (25,35,45)

db.test.find().sort({'ID':-1})                  <==>          select * from test order by IDdesc

db.test.distinct('name',{'ID':{$lt:20}})   <==>          select distinct(name) from testwhere ID<20

db.test.group({key:{'name':true},cond:{'name':'foo'},reduce:function(obj,prev){prev.msum+=obj.marks;},initial:{msum:0}})     <==>     select name,sum(marks) from testgroup by name

db.test.find('this.ID<20',{name:1})        <==>           select name from test whereID<20

db.test.insert({'name':'foobar','age':25})    <==>       insertinto test ('name','age') values('foobar',25)

db.test.remove({})                                     <==>       delete * from test

db.test.remove({'age':20})                        <==>       delete test where age=20

db.test.remove({'age':{$lt:20}})                <==>        delete test where age<20

db.test.remove({'age':{$lte:20}})              <==>        delete test where age<=20

db.test.remove({'age':{$gt:20}})              <==>         delete test where age>20

db.test.remove({'age':{$gte:20}})            <==>         delete test where age>=20

db.test.remove({'age':{$ne:20}})             <==>         delete test where age!=20

db.test.update({'name':'foobar'},{$set:{'age':36}})    <==>    update test set age=36 where name='foobar'

db.test.update({'name':'foobar'},{$inc:{'age':3}})     <==>     update test set age=age+3 where name='foobar'

模糊查询：$regex

db.test.find({"name":{$regex:"aaa"}})

分组个数过滤

db.getCollection('id_mapper').aggregate([{$group:{ _id :"$contract_id",count:{$sum:1}}},{$match:{count:{$gt:1}}}])

判断是否为空

db.getCollection('id_mapper').find({"sinocardid":{$in:[null]}})