MongoDB limit 选取 skip跳过 sort排序 方法

Posted 2021-02-16 minger_lcm

 

MongoDB  limit 选取 skip跳过 sort排序

在mysql里有order by  MongoDB用sort代替order by

 

> db.user.find()
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }
{ "_id" : ObjectId("5ca7a4c4219efd687462f969"), "id" : 5, "name" : "ben", "age" : 24 }
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }

 

Limit 选取 :

我要从这些 Document 中取出多少个

选取2条Document

> db.user.find().limit(2)
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }

从整个collection集合的第一条数据Document开始选取两条

 

Skip 跳过 :

我要跳过多少个Document

我要跳过前两个 Document 直接从第三个Document 开始

 

> db.user.find().skip(2)
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }
{ "_id" : ObjectId("5ca7a4c4219efd687462f969"), "id" : 5, "name" : "ben", "age" : 24 }
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }

skip(2) 就是跳过两条Document，从整个collection集合第一条数据Document开始跳过

 

 

Limit + Skip : 

我只想要第二条和第三条

> db.user.find()
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }
{ "_id" : ObjectId("5ca7a4c4219efd687462f969"), "id" : 5, "name" : "ben", "age" : 24 }
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }
> 
> db.user.find().skip(1).limit(2)
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }

跳过第一条数据，从第二条数据开始选取2条数据Document

 

反过来顺序是一样的

> db.user.find().limit(2).skip(1)
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }

选取两条数据，但要跳过第一条数据，从第二条数据开始选取

 

Sort 排序 : 将结果按照关键字排序

sort写法  {} 里面根据什么Field进行排序 

1 为升序 , -1 为降序

 

db.user.find().sort({ sortField:-1 })

 

 

 将find出来的Document 按照 age 进行 升序 | 降序 排列

升序

> db.user.find().sort({"age":1})
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f969"), "id" : 5, "name" : "ben", "age" : 24 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }

降序

> db.user.find().sort({"age":-1})
{ "_id" : ObjectId("5ca7a4b7219efd687462f966"), "id" : 2, "name" : "mike", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }
{ "_id" : ObjectId("5ca7a4c4219efd687462f969"), "id" : 5, "name" : "ben", "age" : 24 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f967"), "id" : 3, "name" : "peter", "age" : 21 }

 

 Limit + Skip + Sort 混搭:

选取第二条第三条第四条 并 按照 age 进行 降序排列

> db.user.find().skip(1).limit(3).sort({age:-1})
{ "_id" : ObjectId("5ca7a505219efd687462f96a"), "id" : 6, "name" : "Mary", "age" : 84, "gender" : "男" }
{ "_id" : ObjectId("5ca7a4b0219efd687462f965"), "id" : 1, "name" : "jack", "age" : 73 }
{ "_id" : ObjectId("5ca7a4c4219efd687462f968"), "id" : 4, "name" : "xiaogang", "age" : 34, "hobby" : [ "羽毛球", "篮球", "足球" ] }