Notes

use dbname;
show dbs;
db.createCollection('stud');
db.stud.insertMany([{"name":"demo"},{"name":"temp"}]);
db.stud.find().pretty();
db.stud.find({},{"name":1,"_id":0});
db.stud.distinct("city"); //unique cities
db.stud.find({"city":"surat"},{}); //get all the details of who city is surat.
db.stud.find().sort({"enro":-1}) //ascending order
db.stud.find().limit(5) //first five data
db.stud.find().skip(db.stud.count()-3) //last three data
db.stud.update({"name":"demo"},{$set:{"dob":"06/01/1922"}}); //set
db.stud.update({"name":"demo"},{$unset:{"dob":"06/01/1922"}}); //unset
db.stud.find( { $or: [ { quantity: { $lt: 20 } }, { price: 10 } ] } ) //or ,and,lt,gt,eq,lte,gte
db.stud.remove({"city":"vapi"})//remove details who city is vapi
db.stud.find({"name":{$regex:"^.a"}},{_id:0}) //second letter is 'a'
db.stud.count() //count number of data
db.stud.distinct("city").length //total number of city
db.stud.updateMany({},{$inc:{"marks":10}});
db.stud.updateMany({},{$mul:{"price":1.5}});
db.stud.aggregate({$group:{_id:0,min:{$min:'$marks'},max:{$max:'$marks'}}});
db.stud.aggregate({$group:{_id:0,avg_marks:{$avg:'$marks'}}});
db.Items.aggregate({$project:{_id:0,msg:{$concat:["$name","price is ",{ $toString: "$price" }]}}})//display msg custome
db.Items.aggregate({$project:{_id:0,msg:{$concat:["The","$name"," stock date is ",stockdate:{$dateToString: { format: "%Y-%m-%d", date: "$stockdate"}}]}}})
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Array
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db.emp_count.insertOne({"emp_name":"ABC", "emp_skills": [["PostgreSQL", "MongoDB", "MySQL", "Perl","ORACLE"]]});
db.stud_test.find ({results: {$all: [88]}}) //display all the filed form array
db.stud_test.find({results: {$elemMatch: {$gte: 80, $lt: 95}}}) //only match given critria
db.stud_test.find ({“results": {$size: 3}}); //three recoreds show
db.stud_test.updateOne ({stud_id: 1, results: 85},{$set: {"results.$" : 95 }}) // identify array element and update the same into the collection
db.stud_test.updateOne( { stud_id: 1 }, { $pop: { results: -1 } } ) //remove the first and last element from an array
db.stud_test.update( { stud_id: 1 }, { $pull: { results: { $gte: 95 } } } ) // is used to remove elements from an existing array.
db.stud_test.update ({stud_id: 1}, { $push: { results: 101 }}) //push the element
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import and export
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sudo mongoimport --db newdb --collection restaurants --file primer-dataset.json
sudo mongoexport --db newdb -c restaurants --out newdbexport.json

--or-- run both import and export outside mongo shell
mongimport --db<dbname> --collection<cname> --file filename.json
-> mongoimport --jsonArray --db newDB --collection stud --file /stud.json

mongoexport
mongoexport --db<dbname> --collection<cname> --file filename.json
-> mongoexport --db mydb --collection emp --type=CSV --fields name,age,salary --out
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mapReduce
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var map=function(){ emit(this.age,this.rank)};
var reduce=function(age,rank){ return Array.sum(rank);}; //Array.avg(rank)
db.employee.mapReduce(map,reduce,{out :"resultCollection1"});
db.resultCollection1.find()