MongoDB distinct() Operator

In MongoDB, distinct() is used to find unique values of a particular field from a collection. It returns the unique values in an array.

Syntax

db.collection.distinct("fieldName")

Example: Employee Collection

Suppose emp contains:

{ empno: 1, ename: "Amit",   dept: "IT",    salary: 25000 }
{ empno: 2, ename: "Ravi",   dept: "HR",    salary: 30000 }
{ empno: 3, ename: "Neha",   dept: "IT",    salary: 28000 }
{ empno: 4, ename: "Raj",    dept: "Sales", salary: 35000 }
{ empno: 5, ename: "Priya",  dept: "HR",    salary: 32000 }

1. Find distinct departments

db.emp.distinct("dept")

Output:

[ "IT", "HR", "Sales" ]

Even though IT and HR occur multiple times, they are returned only once.

2. Find distinct employee names

db.emp.distinct("ename")

Output:

[ "Amit", "Ravi", "Neha", "Raj", "Priya" ]

3. Distinct with a condition

You can provide a query as the second argument. MongoDB’s syntax is:

db.collection.distinct("field", { condition })

For example, find distinct departments where salary is greater than 28000:

db.emp.distinct("dept", { salary: { $gt: 28000 } })

Output:

[ "HR", "Sales" ]

4. Distinct values of salary

db.emp.distinct("salary")

Output:

[ 25000, 30000, 28000, 35000, 32000 ]

5. Distinct values from an array

If documents contain:

{ name: "A", skills: ["Java", "MongoDB"] }
{ name: "B", skills: ["Python", "MongoDB"] }
{ name: "C", skills: ["Java", "PHP"] }

Then:

db.student.distinct("skills")

returns:

[ "Java", "MongoDB", "Python", "PHP" ]

MongoDB treats array elements as individual values for distinct().

⭐ Important Difference