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(2). No error will be reported if the data does not exist , It will be recorded in memory , If you use add data operation , This database will be created

(3). If before executing other orders , You did not add data , Then the memory will be released

use UserName

5. Create table

createCollection Parameters	The default value is
Table name	nothing

db.createCollection("students")

6. Delete table

db.students.drop()

7. insert data

insert Parameters	The default value is
JOSN Array or single JSON	nothing

If this table is not saved, it will be automatically created

 db.students.insert({name:" Zhang San ",age:18,gender:" male "})

db.students.insert([{name:" Wang Wu ",age:15,gender:" male "},{name:" Li Si ",age:19,gender:" male "}])

8. Delete table data

Delete a piece of data and return the object	findOneAndDelete Parameters	The default value is
Delete a piece of data and return the object	1. Delete the condition	nothing

Only one piece of data can be deleted	deleteOne Parameters	The default value is
Only one piece of data can be deleted	1. Delete the condition	nothing

Delete multiple data	deleteMany Parameters	The default value is
Delete multiple data	1. Delete the condition	nothing

remove Parameters	The default value is
1. Delete the condition	nothing
2. Whether to delete only one	false

by {} It means to clear all data in the table

db.students.remove({})

Delete all in the table name For Zhang San's data

db.students.remove({"name":" Zhang San "})

Delete the specified id data

 db.students.remove({_id:ObjectId("6208af4dd5f0203f271bb2fa")})

9. Query a piece of data in the table

findOne Parameters	The default value is
Query criteria	nothing

db.students.findOne()

10. Query all data in the table

find Parameters	The default value is
Query criteria	nothing

db.students.find()

11. Query the specified quantity data in the specified location table

(1). db.students.find().skip(2)

(2). dskip(2) Put the starting position inside , That is, query from the third data

(3).limit(5) How many pieces of data are extracted , Here are five pieces of data

db.students.find().skip(2)

db.students.find().skip(2).limit(5)

12. Query table Condition display data

(1). db. Table name .find()

(2). The first query condition {}, Empty means to display all data

(3). The second display condition {age:1},0 No display ,1 Show , Comma separated conditions

(4). This order is , All data is only displayed age data , If the display condition is 0 Will only be displayed except age All data except data

db.students.find({},{age:1})

13. Condition query table data

(1). db. Table name .find()

(2). The first query condition {}, Empty means to display all data , Comma separated

(3). Inquire about name For all the data of Zhang San

(4). Inquire about name For Zhang San ,age by 18 Full data

db.students.find({name:" Zhang San "})

 db.students.find({name:" Zhang San ",age:18})

14. Fuzzy / Regular query table data

(1). db. Table name .find() perhaps db. Table name .findOne() This can only be queried

(2). Inquire about name There are pieces of data in it ,/ Regular expressions /

db.students.find({name:/ Zhang /})

db.students.find({name:/^[a-z]{4}$/})

15. Operator queries table data

(1). db. Table name .find() perhaps db. Table name .findOne() This can only be queried

(2). The first query condition {}, Empty means to display all data , Comma separated

(3). The conditions say Json,Json Write operators in ,（$and and $or） exception , Here is a case

Operator
also	$and
perhaps	$or
Greater than	$gt
Less than	$lt
It's not equal to	$ne
Greater than or equal to	$gte
Less than or equal to	$lte
Include conditions	$in
No conditions are included	$nin

Inquire about age be equal to 15 also gender Equal to a man , The following two implementation methods are the same

db.students.find({$and:[{age:15,gender:" male "}]})

db.students.find({$and:[{age:15},{gender:" male "}]})

Inquire about age be equal to 15 perhaps gender Equal to a man , Multiple Json

db.students.find({$or:[{age:15},{gender:" male "}]})

The query is greater than 20 Of

 db.students.find({age:{$gt:20}})

Query is greater than or equal to 20 Of

db.students.find({age:{$gte:20}})

Query less than... Etc 20 Of

db.students.find({age:{$lt:20}})

Query is less than or equal to 20 Of

db.students.find({age:{$lte:20}})

Inquiry is not equal to 20 Of

db.students.find({age:{$ne:20}})

The query contains 20,19,15 Of

db.students.find({age:{$in:[20,19,15]}})

The query does not contain 20,19,15 Of

db.students.find({age:{$in:[20,19,15]}})

16. Query the table data and sort and display

sort Parameters		value
Sort parameters	Ascending	1
Sort parameters	Descending	-1

Fuzzy search for data with Zhang characters to sort in ascending order

db.students.find({name:/ Zhang /}).sort({age:1})

Fuzzy search of data with Zhang characters for multiple conditional sorting , Multiple sort ！

db.students.find({name:/ Zhang /}).sort({age:1,height:-1})

17. modify / Delete the attribute data specified in the table

update Parameters	Parameter format	The default value is
1. filter	Json Format	nothing
2. Modified properties	Json Format	nothing
3. Whether to create	Boolean value	false
4. Whether to modify in batch	Boolean value	false

The operator	effect
$set	modify
$unset	Delete
$inc	Self increasing
$push	Add members to the array
$each	coordination $push Add multiple members
$pop	Pop up tail members
$pull	Delete the specified member

(1). $set Modify the specified properties

Here is the handle. name For Zhang San's age Attribute to 18, Other properties will not be deleted

db.students.update({name:" Zhang San "},{$set:{age:20}})

Here is to put all less than or equal to 18 Of age Attribute to 18, Other properties will not be deleted

db.students.update({age:{$lte:18}},{$set:{age:19}},false,true)

(2). $unset Delete the specified attribute

Here is the handle. name For Zhang San's age Attribute removed , And do not delete other attributes

db.students.update({name:" Zhang San "},{$unset:{age:19}})

Note the addition operator $unset, Otherwise, his attribute will be cleared

Here is the handle. name For Zhang San's age Attribute to 18, And all other attributes will be deleted

db.students.update({name:" Zhang San "},{age:20})

(3). $inc Auto increment specified attribute

The operator $inc send age Self increase on the original basis 2

db.students.update({name:" Zhang San "},{$inc:{age:2}})

(4). $set $inc $unset Use a combination of Auto add, delete and modify

$set $inc $unset Use a combination of ,age Self increasing 2,gender Change to female , hold name Property deleted

db.students.update({name:" Zhang San "},{$inc:{age:2},$set:{gender:" Woman "},$unset:{name:""}})

(5). $push Add members to the specified attribute array ,$each Add multiple members at once

The operator $push likes Array added new members

db.students.update({name:" Zhang San "},{$push:{likes:" sleep "}})

add $each, You can add multiple members at a time

db.students.update({name:" Zhao Liuliu "},{$push:{likes:{$each:[" sleep "," To play basketball "," running "]}}})

(6). $pop Pop up a member at the end of the specified attribute array

db.students.update({name:" Zhang San "},{$pop:{likes:1}})

(6). $pull Delete the specified member from the specified attribute array

db.students.update({name:" Zhang San "},{$pull:{likes:" sleep "}})

18. polymerization

aggregate The operator	effect
$group	Perform distributed query ,( Such as the statistical average , Make a peace, etc )
$match	By specifying attributes matching / Filter
$unwind	split array , Form each array into a new JSON data
$project	(1 Display only /0 Not shown ) Some attribute , Modify display name

_id	Grouping properties , It can be for null
$sum	similar Js in reduce() Cumulative sum of functions
$max	For maximum
$avg	averaging
$push	Add to array
$concat	Multi attribute concatenation string

Operator
also	$and
perhaps	$or
Greater than	$gt
Less than	$lt
It's not equal to	$ne
Greater than or equal to	$gte
Less than or equal to	$lte
Include conditions	$in
No conditions are included	$nin

(1). $sum Application

This is equivalent to that I put score Add values of attributes , Get the total

db.students.aggregate([
   {
   $group: {
     _id: null,
     count: {
       $sum: "$score"
     }
   }}
])

use cname Attribute to group , And calculate the score Total attribute value

db.students.aggregate([
   {
   $group: {
     _id: "$cname",
     count: {
       $sum: "$score"
     }
   }}
])

group use cname Attribute and

math To match cname Attribute is equal to the ( In grade one ), And calculate the score Total attribute value

db.students.aggregate([
    {$match: {cname:" In grade one "}},
   {
   $group: {
     _id: "$cname",
     count: {
       $sum: "$score"
     }
   }}
])

If match Later, you need to change the condition to _id

group use cname Attribute grouping and calculate the score Total attribute value , use math To filter lower than or equal to 300 The data of

Because the cumulative results are given above count all ,match I also need to write count Used for filtration

db.students.aggregate([
   {$group: {
     _id: "$cname",
     count: {
       $sum: "$score"
     }
    }},{$match: {count:{$gte:300}}},
])

(2). $max Application

seek score The highest value in the attribute

db.students.aggregate([
   {$group: {
     _id:null,
     count: {
       $max: "$score"
     }
    }}
])

First use cname Attribute to group , In use max Let's ask each group score The highest value of the attribute

db.students.aggregate([
   {$group: {
     _id: "$cname",
     count: {
       $max: "$score"
     }
    }}
])

(3). $avg Application

First use cname Attribute to group , In use avg Let's ask each group score The average value of an attribute

db.students.aggregate([
   {$group: {
     _id:"$cname",
     count: {
       $avg: "$score"
     }
    }}
])

(4). First use cname Attribute to group , In use push hold score Add the value of the property to the array

db.students.aggregate([
   {$group: {
     _id:"$cname",
     count: {
       $push: "$score"
     }
    }}
])

(3). $unwind Application

First insert an array of data into the table

db.students.insert({name:" Zhang San ",age:19,gender:" Woman ",cname:" Third grade ",interset:[" having dinner "," sleep "," running "]})

First use match Filter , In use $unwind by $interset Split into new data

db.students.aggregate([
    {
        $match: {
          name:" Zhang San "
        }
    },
   {
       $unwind: "$interset"
   }
])

(4). $project Application

hold _id Property does not display ,1 To display only this attribute ,0 To not display this attribute

db.students.aggregate([
    {
        $match: {
          name:" Zhang San "
        }
    },
   {
       $unwind: "$interset"
   },{
       $project: {
         _id:0
       }
   }
])

Here is only id and name, The difference is that I put name The display is changed to username

db.students.aggregate([
    {
        $match: {
          name:" Zhang San "
        }
    },
   {
       $unwind: "$interset"
   },{
       $project: {
         _id:1,
         username:"$name"
       }
   }
])

(5). $concat Application

$concat Concatenate the attributes and strings in the array

db.students.aggregate([
    {
        $match: {
          name:" Zhang San "
        }
    },
   {
       $unwind: "$interset"
   },{
       $project: {
         _id:1,
         info:{$concat:["$name","----","$cname"]}
       }
   }
])

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