Table of Contents
In MongoDB, you can use the aggregate function to select distinct values from multiple fields by specifying the distinct keyword followed by the fields you want to select. The aggregate function will return a list of distinct values for each of the specified fields. Additionally, you can use the $project operator to limit the fields that are included in the result set.
You can use the following syntax to select distinct values from multiple fields in MongoDB:
db.collection.aggregate(
[
{$group: { "_id": { field1: "$field1", field2: "$field2" } } }
]
)
The following examples show how to use this syntax with a collection teams with the following documents:
db.teams.insertOne({team: "Mavs", position: "Guard", points: 31})
db.teams.insertOne({team: "Mavs", position: "Guard", points: 22})
db.teams.insertOne({team: "Rockets", position: "Center", points: 19})
db.teams.insertOne({team: "Rockets", position: "Forward", points: 26})
db.teams.insertOne({team: "Rockets", position: "Forward", points: 29})
db.teams.insertOne({team: "Cavs", position: "Guard", points: 33})
Example: Select Distinct Values from Multiple Fields
We can use the following query to find all of the distinct values from the team and position fields:
db.teams.aggregate(
[
{$group: { "_id": { team: "$team", position: "$position" } } }
]
)
This query returns the following documents:
{ _id: { team: 'Mavs', position: 'Guard' } }
{ _id: { team: 'Rockets', position: 'Forward' } }
{ _id: { team: 'Rockets', position: 'Center' } }
{ _id: { team: 'Cavs', position: 'Guard' } }
And we can use the following query to find all of the distinct values from the team, position, and points fields:
db.teams.aggregate(
[
{$group: {"_id": {team: "$team", position: "$position", points: "$points"}}}
]
)
This query returns the following documents:
{ _id: { team: 'Cavs', position: 'Guard', points: 33 } }
{ _id: { team: 'Rockets', position: 'Forward', points: 29 } }
{ _id: { team: 'Mavs', position: 'Guard', points: 22 } }
{ _id: { team: 'Rockets', position: 'Forward', points: 26 } }
{ _id: { team: 'Mavs', position: 'Guard', points: 31 } }
{ _id: { team: 'Rockets', position: 'Center', points: 19 } }
Notice that all of the documents are returned since there are no two documents that have identical values for the team, position, and points fields.
The following tutorials explain how to perform other common operations in MongoDB: