2020MongoDB基本命令-R操作（查）

全部操作过程
2020MongoDB基本命令-C操作（增）
2020MongoDB基本命令-R操作（查）

1. 基本语句

   db.集合名.find([条件]，[查询的列])
   

   条件
   查询所有数据 {}或者不写
   查询age=10,性别为男 {age:10,sex=‘男’}
   查询的列(可选)
   {age:1}只显示age列
   {age:0}除了age其余的都显示
   无论写什么，_id都会存在

   示例1.(查询数据库中所有的数据)

   //使用test2数据库
   use test2
   // 查询所有集合
   show collections
   db.c1.find()
   

   结果1.

   { “_id” : ObjectId(“5fc22f77451fb8b5be3c3f6e”), “uname” : “ppl”, “age” : 18 }
   { “_id” : 1, “uname” : “ppl”, “age” : 18 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f6f”), “username” : “a1”, “age” : 99 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f70”), “username” : “a2”, “age” : 89 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f71”), “username” : “a3”, “age” : 79 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f72”), “uname” : “b0”, “age” : 50 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f73”), “uname” : “b1”, “age” : 51 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f74”), “uname” : “b2”, “age” : 52 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f75”), “uname” : “b3”, “age” : 53 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f76”), “uname” : “b4”, “age” : 54 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f77”), “uname” : “b5”, “age” : 55 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f78”), “uname” : “b6”, “age” : 56 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f79”), “uname” : “b7”, “age” : 57 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7a”), “uname” : “b8”, “age” : 58 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7b”), “uname” : “b9”, “age” : 59 }

   示例2.（查询uname列）

   db.c1.find({},{uname:1})
   

   结果2.

   { “_id” : ObjectId(“5fc22f77451fb8b5be3c3f6e”), “uname” : “ppl” }
   { “_id” : 1, “uname” : “ppl” }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f6f”) }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f70”) }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f71”) }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f72”), “uname” : “b0” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f73”), “uname” : “b1” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f74”), “uname” : “b2” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f75”), “uname” : “b3” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f76”), “uname” : “b4” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f77”), “uname” : “b5” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f78”), “uname” : “b6” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f79”), “uname” : “b7” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7a”), “uname” : “b8” }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7b”), “uname” : “b9” }

   示例3.(查询除了uname以外的其余的列)

   db.c1.find({},{uname:0})
   

   结果3.

   { “_id” : ObjectId(“5fc22f77451fb8b5be3c3f6e”), “age” : 18 }
   { “_id” : 1, “age” : 18 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f6f”), “username” : “a1”, “age” : 99 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f70”), “username” : “a2”, “age” : 89 }
   { “_id” : ObjectId(“5fc23651451fb8b5be3c3f71”), “username” : “a3”, “age” : 79 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f72”), “age” : 50 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f73”), “age” : 51 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f74”), “age” : 52 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f75”), “age” : 53 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f76”), “age” : 54 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f77”), “age” : 55 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f78”), “age” : 56 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f79”), “age” : 57 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7a”), “age” : 58 }
   { “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7b”), “age” : 59 }

2.运算符

运算符	功能
$gt	大于
$gte	大于等于
$lt	小于
$lte	小于等于
$in	in
$nin	not in

示例1. 查询年龄大于55岁的用户

db.c1.find({age:{$gt:55}})

结果1.

{ “_id” : ObjectId(“5fc23651451fb8b5be3c3f6f”), “username” : “a1”, “age” : 99 }
{ “_id” : ObjectId(“5fc23651451fb8b5be3c3f70”), “username” : “a2”, “age” : 89 }
{ “_id” : ObjectId(“5fc23651451fb8b5be3c3f71”), “username” : “a3”, “age” : 79 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f78”), “uname” : “b6”, “age” : 56 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f79”), “uname” : “b7”, “age” : 57 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7a”), “uname” : “b8”, “age” : 58 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7b”), “uname” : “b9”, “age” : 59 }

示例2.查询用户年龄在55，57，79岁的信息

db.c1.find({age:{$in:[55,57,59]}})

结果2.

{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f77”), “uname” : “b5”, “age” : 55 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f79”), “uname” : “b7”, “age” : 57 }
{ “_id” : ObjectId(“5fc238ac451fb8b5be3c3f7b”), “uname” : “b9”, “age” : 59 }