Preparing data

db.stu.insert({name:'Guo Jing',hometown:'Mongolia',age:20,gender:true})
db.stu.insert({name:'Huang Rong',hometown:'Taohua Island',age:18,gender:false})
db.stu.insert({name:'Yang Kang',hometown:'daikin',age:20,gender:true})
db.stu.insert({name:'Mu Nianchi',hometown:'Song',age:18,gender:false})
db.stu.insert({name:'evil east',hometown:'Taohua Island',age:40,gender:true})
db.stu.insert({name:'West Poison',hometown:'Western Regions',age:41,gender:true})
db.stu.insert({name:'Southern Imperial',hometown:'Dali',age:42,gender:true})
db.stu.insert({name:'Northern Beggar',hometown:'Song',age:45,gender:true})
db.stu.insert({name:'Small armor',hometown:'Song',age:45,gender:false})
db.stu.insert({name:'Central Divinity',hometown:'quanzhen sect',age:44,gender:true})

Basic Query

• Method find()

  db. Collection name. find({condition document})

• Method findOne() query, returning only the first

  db. Collection name. findOne({conditional document})

  

• Method pretty() formats the result

  db. Collection name. find({conditional document}). pretty()

  

Comparison operator

• Equivalent, default is equal to judgement, no operator

  db.stu.find({age:18}) //Query all ages18Students

• Less than: $lt

  db.stu.find({age:{$lt:18}})  //Query students younger than 18

• Less than or equal to: $lte

  db.stu.find({age:{$lte:18}}) //Inquiry for students younger than or equal to 18

• Greater than: $gt

  db.stu.find({age:{$gt:18}})  //Search for students older than 18

• Greater than or equal to: $gte

  db.stu.find({age:{$gte:18}})  //Students with queries greater than or equal to 18

• Not equal to: $ne

  db.stu.find({age:{$ne:18}})   //Inquiry age is not equal to 18 students

Logical Operator

• There are many conditions when querying, and the connection between them needs to be done by logical operators.

• Logic and: The default is the relationship between logic and

  // Query age greater than or equal to18，And the gender istrueStudents
  db.stu.find({age:{$gte:18},gender:true})

  

• Logic or: Use $or, with an array of values, each element in the array is json

  // Query age is older than18，Or sexfalseStudents
  db.stu.find({$or:[{age:{$gt:18}},{gender:false}]})

  

• and with or

  // Query age is older than18Or sextrueThe student, and the student's name is Guo Jing.
  db.stu.find({$or:[{age:{$ge:18}},{gender:true}],name:'Guo Jing'})

  

Range operator

• Use $in,$nin to determine whether or not within a certain range

  // Query age is18,28Students
  db.stu.find({age:{$in:[18,28]}})

  

Regular Expression Query

• The terminal shell provided by mongodb is also an executor of js, which can write JS code and functions

• Use //or $regex to write regular expressions

  // Inquiry for classmates surnamed Huang
  db.stu.find({name:/^yellow/})
  db.stu.find({name:{$regex:'^yellow'}})

  

Custom Query

• Write a function after $where to return data that meets the criteria

  db.stu.find(
  {
      $where: function(){
        return this.age>30
      }
  }
  )

  

Limit and skip

• limit(): Used to read a specified number of documents

  db. Collection name. find().limit(number)

  • Parameter number: Indicates the number of entries to read the document
  • Display all documents in the collection without specifying Number

  // Show the first two students'information
  db.stu.find().limit(3)

  

• Skip: Used to skip a specified number of documents

  db. Collection name. find().skip(number)

  • The parameter number represents the number of records skipped, with a default value of 0

• limit and skip can be used together, regardless of order.

Projection

• In the return result of the query, only the necessary fields are selected, not the whole field of a document.

• Grammar:

  // The parameters are fields and values, the value is 1 for display, and the value is 0 for non-display.
  db. Collection name. find({}, {field name: 1,...})

• For fields that need to be displayed, set to 1, or not to display

• Special: For the _id column, it is displayed by default. If it is not displayed, it needs to be explicitly set to 0.

sort

• Method sort(), which is used to sort the result set

  db. Collection name. find().sort({field: 1,...})

• Parametric 1 is ascending order

• Parameter - 1 is descending order

  // Sort age from small to large
  db.stu.find({},{name:1,age:1}).sort({age:1})

  

Number of Statistics

• Method count() is used to count the number of documents in the result set

  db. Collection name. find({condition}). count()
  db. Collection name. count({condition})

• Example

  // Statistical age is greater than18 Total number
  db.stu.find({age:{$gt:18}}).count()
  db.stu.count({age:{$gt:18}})

  

Eliminate duplication

• Method distinct() to de-duplicate data

  db. Collection name. distinct('de-duplicate field', {condition})

• Example:

  // Look for students older than 18 and which provinces they come from
  db.stu.distinct('hometown',{age:{$gt:18}})