Contents of page >
- 1.1) First, Let's create new collection and insert document >
- 1.2) FIND > Query all documents of collection using find() method>
- 2.1) We will group employee by firstName and find count of of each group.
- 2.2) Sql query equivalent to above MongoDB query is >
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 })
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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()
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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 }
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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}}}])
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Output >
{ "_id" : "neh", "countOfEmp" : 1 }
{ "_id" : "sag", "countOfEmp" : 2 }
{ "_id" : "ank", "countOfEmp" : 2 }
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2.2) Sql query equivalent to above MongoDB query is >
select firstName, count(*) countOfEmp
from employee
group by firstName;
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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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