mongodb条件查询（二）

> db.c1.find({},{_id:0}){ "name" : "John", "age" : 20, "sex" : "M" }{ "name" : "Tom", "age" : 21, "sex" : "F" }{ "name" : "Davi", "age" : 20, "sex" : "F" }{ "name" : "Lily", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M", "hobby" : [ "music", "sport" ] }{ "name" : "Smith", "age" : 21, "sex" : "F", "hobby" : null }{ "name" : "Sam", "age" : 20, "sex" : "F", "hobby" : [ "swimming" ] }

1、文档数（即记录数）

> db.c1.count()8> db.c1.find().count()8

2、返回的前多少条记录，如下返回前两条记录

> db.c1.find({},{_id:0}).limit(2){ "name" : "John", "age" : 20, "sex" : "M" }{ "name" : "Tom", "age" : 21, "sex" : "F" }

3、返回记录的起点，如下跳过前6条记录，从第7条开始

> db.c1.find({},{_id:0}).skip(6){ "name" : "Smith", "age" : 21, "sex" : "F", "hobby" : null }{ "name" : "Sam", "age" : 20, "sex" : "F", "hobby" : [ "swimming" ] }

4、排序，如下1为升序，-1为降序

> db.c1.find({},{_id:0}).sort({age:1}){ "name" : "John", "age" : 20, "sex" : "M" }{ "name" : "Davi", "age" : 20, "sex" : "F" }{ "name" : "Sam", "age" : 20, "sex" : "F", "hobby" : [ "swimming" ] }{ "name" : "Tom", "age" : 21, "sex" : "F" }{ "name" : "Smith", "age" : 21, "sex" : "F", "hobby" : null }{ "name" : "Lily", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M", "hobby" : [ "music", "sport" ] }> db.c1.find({},{_id:0}).sort({age:1,name:-1}){ "name" : "Sam", "age" : 20, "sex" : "F", "hobby" : [ "swimming" ] }{ "name" : "John", "age" : 20, "sex" : "M" }{ "name" : "Davi", "age" : 20, "sex" : "F" }{ "name" : "Tom", "age" : 21, "sex" : "F" }{ "name" : "Smith", "age" : 21, "sex" : "F", "hobby" : null }{ "name" : "Lucy", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M", "hobby" : [ "music", "sport" ] }{ "name" : "Lily", "age" : 22, "sex" : "M" }

5、分页，同时使用上述三种函数实现，如下分别人第一页两条，第二页两条

> db.c1.find({},{_id:0}).limit(2).sort({name:1}){ "name" : "Davi", "age" : 20, "sex" : "F" }{ "name" : "John", "age" : 20, "sex" : "M" }> db.c1.find({},{_id:0}).skip(2).limit(2).sort({name:1}){ "name" : "Lily", "age" : 22, "sex" : "M" }{ "name" : "Lucy", "age" : 22, "sex" : "M" }

6、随机查询，可使用随机函数Math.random()，例：从一个集合中随机抽取一条记录

<pre name="code" class="sql">> Math.random()0.06595390615984797> rdm=Math.floor(Math.random()*db.c1.count())  #Math.floor取整2> db.c1.find({},{_id:0}).skip(rdm).limit(1){ "name" : "Davi", "age" : 20, "sex" : "F" }