Find count of all employee by group in collection in MongoDB

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1) First let's create insert documents in collection in MongoDB


1.1) First,​ ​Let's​ ​create​ ​new​ ​collection​ ​and​ ​insert​ ​document​ ​>
db.employee.insert({_id : 1,  firstName:"ank", salary : 1000 })
db.employee.insert({_id : 2,  firstName:"ank", salary : 2000 })
db.employee.insert({_id : 3,  firstName:"sag", salary : 3000 })
db.employee.insert({_id : 4,  firstName:"sag", salary : 4000 })
db.employee.insert({_id : 5,  firstName:"neh", salary : 5000 })
Above will create collection (or table) (if collection already exists it will insert documents in it).


1.2) FIND > Query all documents of collection using find() method>
db.employee.find()
Output>
{ "_id" : 1, "firstName" : "ank", "salary" : 1000 }
{ "_id" : 2, "firstName" : "ank", "salary" : 2000 }
{ "_id" : 3, "firstName" : "sag", "salary" : 3000 }
{ "_id" : 4, "firstName" : "sag", "salary" : 4000 }
{ "_id" : 5, "firstName" : "neh", "salary" : 5000 }

2) Find count of all employee with same firstName in collection in MongoDB >


2.1) We will group employee by firstName and find count of of each group.
We will aggregate() method and $group operator.
db.employee.aggregate([{$group : {_id : "$firstName", countOfEmp : {$sum : 1}}}])
Output >
{ "_id" : "neh", "countOfEmp" : 1 }
{ "_id" : "sag", "countOfEmp" : 2 }
{ "_id" : "ank", "countOfEmp" : 2 }


2.2) Sql query equivalent to above MongoDB query is >
select firstName, count(*) countOfEmp
from employee
group by firstName;




3) Summary -
So in this MongoDB tutorial we learned how to Find count of all employee by group in collection in MongoDB


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RELATED LINKS>

What is MongoDB - A quick introduction to database

Create new database in mongoDB

How to Drop collection in MongoDB

Create new collection(table) in mongoDB


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