How to query for records where field is null or not set in MongoDB?

Let us work around two cases −

Case 1 − The syntax is as follows when the field is present and set to null.

db.yourCollectionName.count({yourFieldName: null});

Case 1 − The syntax is as follows when the field is not present and not set.

db.yourCollectionName.count({yourFieldName: {$exists: false}});

To understand both the above syntaxes, let us create a collection with the document. The query to create a collection with a document is as follows −

> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Larry","EmployeeAge":null,"EmployeeSalary":18500});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a995c6cea1f28b7aa07fe")
}
> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Bob","EmployeeAge":21,"EmployeeSalary":23500});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a99836cea1f28b7aa07ff")
}

> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Carol","EmployeeSalary":45500});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a999b6cea1f28b7aa0800")
}
> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Mike","EmployeeAge":null,"EmployeeSalary":45500});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a99bb6cea1f28b7aa0801")
}
> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Ramit","EmployeeSalary":85500});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c8a99d76cea1f28b7aa0802")
}

Display all documents from a collection with the help of find() method. The query is as follows −

> db.fieldIsNullOrNotSetDemo.find().pretty();

The following is the output −

{
   "_id" : ObjectId("5c8a995c6cea1f28b7aa07fe"),
   "EmployeeName" : "Larry",
   "EmployeeAge" : null,
   "EmployeeSalary" : 18500
}
{
   "_id" : ObjectId("5c8a99836cea1f28b7aa07ff"),
   "EmployeeName" : "Bob",
   "EmployeeAge" : 21,
   "EmployeeSalary" : 23500
}
{
   "_id" : ObjectId("5c8a999b6cea1f28b7aa0800"),
   "EmployeeName" : "Carol",
   "EmployeeSalary" : 45500
}
{
   "_id" : ObjectId("5c8a99bb6cea1f28b7aa0801"),
   "EmployeeName" : "Mike",
   "EmployeeAge" : null,
   "EmployeeSalary" : 45500
}
{
   "_id" : ObjectId("5c8a99d76cea1f28b7aa0802"),
   "EmployeeName" : "Ramit",
   "EmployeeSalary" : 85500
}

Case 1 −

The field EmployeeAge is present and set to null.

The query is as follows −

> db.fieldIsNullOrNotSetDemo.count({EmployeeAge: null});

The following is the output −

4

Case 2 −

The field ‘EmployeeAge’ is not present and not set. The query is as follows −

> db.fieldIsNullOrNotSetDemo.count({EmployeeAge: {$exists: false}});

The following is the output −

2