MongoDB Note 4-query Operation

1. Specify the return key 2, query condition 2.1 comparison operator $lt=

$nephrite =

2.2 query conditions query the names and ages of students aged 25 to 27 db.persons.find ({age: {$gte:25,$lte:27}}, {_ id:0,name:1,age:1}) query the math scores of all students who are not Korean students db.persons.find ({country: {$ne: "Korea"}}, {_ id:0,country:1) Db.persons.find ({country: {$in: ["China", "USA"]}}, {_ id:0,name:1,country:1}) query the name and country db.persons.find ({country: {$nin: ["China", "USA"]}}, {_ id:0,name:1) of students whose nationality is not Chinese or American. Country:1}) 2.4OR queries for information on students whose scores are greater than 85 in Chinese or 90 in English ({$or: [{c: {$gt:85}}, {e: {$gt:90}}]}, {_ id:0,name:1,c:1,e:1}) 2.5NULL finds out that students whose sex is null will first increase the gender of Chinese students by db.persons.update ({country: "China"}, {$set: {sex: "m"}). False,true) perform query operations db.persons.find ({sex: {$in: [null]}}, {_ id:0,country:1}) 2.6 regular query db.persons.find ({name:/zhangsan}, {_ id:0,name:1}) 2.7$ not is used to reverse db.person.find ({name: {$not:/zhang/}}, {_ id:0) Name:1}) 2.8. applications of $all and index query students who like "Mongodb" and "JS" db.persons.find ({books: {$all: ["MONGODB", "JS"]}}, {_ id:0,books:1,name:1}) query information about students whose second book is java db.persons.find ({"books.1": "JAVA"}, {_ id:0,name:1,books:1}) 2.9 query array $size of specified length It cannot be used with comparators. (drawbacks) db.persons.find ({books: {$size:5}}, {_ id:0,name:1}) 2.10 query the 2nd to 4th books on the jim shelf db.persons.find ({name: "jim"}, {books: {$slice: [1m3]}}) 2.11 query the last book db.persons.find ({name: "jim"}, {books: {$slice:-1}, _ id:0) Name:1}) 2.12 document query add educational background document to jim var jim = [{

School: "K"

Score: "A"

}, {

School: "L"

Score: "B"

}, {

School: "J"

Score: "A+"

}]

Db.persons.update ({name: "jim"}, {$set: {school:jim}}) query students who have studied in K db.persons.find ({"school.school": "K"}, {_ id:0,name:1}) db.persons.find ({school: {$elemMatch: {"school": "K"}}, {_ id:0,name:1}) 2.13$ where query age over 22 years old, like reading C++ books We can use $where for complex queries about students who have studied in K School, because he is omnipotent, but we should try to avoid using it less because it will have a performance cost.

Db.persons.find ({"$where": function () {

/ / every document that gets the query result

Var books = this.books

/ / get the school object in the document

Var school = this.school

/ / if age > = 22

If (this.age > 22) {

Var php = null

/ / traversing books

For (var I = 0; I < books.length; iTunes +) {

If (books[ I] = = "C++") {

Php = books [I]

/ / if the school is real

If (school) {

For (var j = 0; j < school.length; jacks +) {

/ / to judge whether to go to school in K or not.

If (school [j] .school = = "K") {

/ / the return is true

Return true

}

}

Break

}

}

}

}

})