Contents of page >
- Step 2.1 - We will group employee by firstName and find maximum salary of each group.
- Step 2.2- We will use aggregate() method, $group operator and $max operator.
- 2.3) Sql query equivalent to above MongoDB query is >
- Step 3.1 - We will group employee by null (nothing) and find maximum salary of group (there will be only 1 group - i.e. whole documents of collection)
- Step 3.2- We will use aggregate() method, $group operator, $max operator and _id : null
- 3.3) Sql query equivalent to above MongoDB query is >
- Find maximum salary of all employee with same firstName where salary > 2000 in collection in MongoDB >
- Step 4.1 - We will find document where salary > 2000
- Step 4.2 - We will use $match operator
- Step 4.3 - Then we will group employee by firstName and find maximum salary of each group.
- Step 4.4 - We will use aggregate() method, $group operator.
- 4.4) Sql query equivalent to above MongoDB query is >
$max operator in MongoDB >
$max operator returns the maximum value from documents in the collection in MongoDB.
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 maximum salary of employee with same firstName in collection in MongoDB >
Step 2.1 - We will group employee by firstName and find maximum salary of each group.
Step 2.2- We will use aggregate() method, $group operator and $max operator.
db.employee.aggregate([{$group : {_id : "$firstName", salary_maximum : {$max : "$salary"}}}])
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Output >
{ "_id" : "ank", "salary_maximum" : 2000 }
{ "_id" : "sag", "salary_maximum" : 4000 }
{ "_id" : "neh", "salary_maximum" : 5000 }
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2.3) Sql query equivalent to above MongoDB query is >
select firstName, max(salary) salary_maximum from employee group by firstName;
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3) Find maximum salary of all employee in collection in MongoDB >
Step 3.1 - We will group employee by null (nothing) and find maximum salary of group (there will be only 1 group - i.e. whole documents of collection)
Step 3.2- We will use aggregate() method, $group operator, $max operator and _id : null
db.employee.aggregate([{$group : {_id : null, salary_maximum : {$max : "$salary"}}}])
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Output >
{ "_id" : null, "salary_maximum" : 5000 }
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3.3) Sql query equivalent to above MongoDB query is >
select max(salary) salary_maximum from employee;
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4) How to write aggregate query with where clause in MongoDB >
Find maximum salary of all employee with same firstName where salary > 2000 in collection in MongoDB >
Step 4.1 - We will find document where salary > 2000
Step 4.2 - We will use $match operator
Step 4.3 - Then we will group employee by firstName and find maximum salary of each group.
Step 4.4 - We will use aggregate() method, $group operator.
db.employee.aggregate([
{ $match: { salary : { $gt: 2000} } },
{$group : {_id : "$firstName", salary_maximum : {$max : "$salary"}}}])
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Output >
{ "_id" : "sag", "salary_maximum" : 4000 }
{ "_id" : "neh", "salary_maximum" : 5000 }
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4.4) Sql query equivalent to above MongoDB query is >
select firstName, max(salary) salary_maximum from employee
where salary > 2000
group by firstName
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5) Summary -
So in this MongoDB tutorial we learned about $max operator in MongoDB. $max operator returns the maximum value from documents in the collection in MongoDB.
Find maximum salary of employee with same firstName in collection in MongoDB >
db.employee.aggregate([{$group : {_id : "$firstName", salary_maximum : {$max : "$salary"}}}])
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Find maximum salary of all employee in collection in MongoDB >
db.employee.aggregate([{$group : {_id : null, salary_maximum : {$max : "$salary"}}}])
|
Find maximum salary of all employee with same firstName where salary > 2000 in collection in MongoDB >
db.employee.aggregate([
{ $match: { salary : { $gt: 2000} } },
{$group : {_id : "$firstName", salary_maximum : {$max : "$salary"}}}])
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