mongDB-- 3. 查询操作

1. 准备工作

(1)启动mongo

　　进入mongo安装目录的bin/ 目录 ， ./mongod

(2)启动mongo客户端

　　./mongo

(3) 查看所有库

show dbs;

(4) 切换到lvyf库

use lvyf

(5) 查看所有的集合

show collections;

(6)从一个集合中查数据

db.first_col.find();

2. 查询

(1) 查看所有 , pretty() 作用就是格式化json数据

db.collection_name.find().pretty();

> db.first_col.find()
{ "_id" : ObjectId("575e879380d09b176a58ce64"), "name" : "lvyafei", "age" : 21, "sex" : "M", "address" : "http://www.lvyf.com" }
{ "_id" : ObjectId("575e880980d09b176a58ce65"), "name" : "chenjl", "age" : 20, "sex" : "W", "address" : "http://www.chenjl.com" }
{ "_id" : ObjectId("575e889880d09b176a58ce66"), "name" : "child", "age" : 2, "sex" : "M", "address" : "http://www.child.com", "status" : "cry and laugh" }

(2) 条件查询

（3）and 条件

根据性别和名字查询记录 ， 对应sql语句where name= ‘lvyafei‘ and sex = ‘M‘

> db.first_col.find({name : "lvyafei" , sex : "M"}).pretty()
{
    "_id" : ObjectId("575e879380d09b176a58ce64"),
    "name" : "lvyafei",
    "age" : 21,
    "sex" : "M",
    "address" : "http://www.lvyf.com"
}

(4) or 条件,语法

db.collection_name.find( { $or :[

{key1 : value1} , {key2 : value2 }

]  } );

根据名字或者性别查询例子：

> db.first_col.find({$or : [ {name:"lvyafei" },{sex : ‘M‘}] })
{ "_id" : ObjectId("575e879380d09b176a58ce64"), "name" : "lvyafei", "age" : 21, "sex" : "M", "address" : "http://www.lvyf.com" }
{ "_id" : ObjectId("575e889880d09b176a58ce66"), "name" : "child", "age" : 2, "sex" : "M", "address" : "http://www.child.com", "status" : "cry and laugh" }

(5) and 和 or 联合使用，相当于 where age >= 3 and ( name=‘lvyafei‘ or sex=‘M‘ )

> db.first_col.find({age : {$gte : 3}, $or:[{name:"lvyafei"} , {set : ‘M‘}]}).pretty()
{
    "_id" : ObjectId("575e879380d09b176a58ce64"),
    "name" : "lvyafei",
    "age" : 21,
    "sex" : "M",
    "address" : "http://www.lvyf.com"
}

(6) 大于和小于联合查询，相当于 where age > 3 and age < 21

> db.first_col.find({"age" : {$lt : 21,$gt:3}})
{ "_id" : ObjectId("575e880980d09b176a58ce65"), "name" : "chenjl", "age" : 20, "sex" : "W", "address" : "http://www.chenjl.com" }

(7) $type操作符

如果要查询 name 是string 类型的记录

> db.first_col.find({name : {$type : 2}});
{ "_id" : ObjectId("575e879380d09b176a58ce64"), "name" : "lvyafei", "age" : 21, "sex" : "M", "address" : "http://www.lvyf.com" }
{ "_id" : ObjectId("575e880980d09b176a58ce65"), "name" : "chenjl", "age" : 20, "sex" : "W", "address" : "http://www.chenjl.com" }
{ "_id" : ObjectId("575e889880d09b176a58ce66"), "name" : "child", "age" : 2, "sex" : "M", "address" : "http://www.child.com", "status" : "cry and laugh" }