Create an Index on a Single Field

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Before You Begin

Procedures
Create an Index on a Single Field
Create an Index on an Embedded Field
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You can create an index on a single field to improve performance for queries on that field. Indexing commonly queried fields increases the chances of covering those queries, meaning MongoDB can satisfy the query entirely with the index, without examining documents.

To create a single-field index, use the db.collection.createIndex() method:

db.<collection>.createIndex( { <field>: 1 } )

Note

Index Sort Order

Using a descending single-field index may negatively impact index performance. For best performance, only use ascending single-field indexes.

Before You Begin

Create a students collection that contains the following documents:

db.students.insertMany( [
   {
      "name": "Alice",
      "gpa": 3.6,
      "location": { city: "Sacramento", state: "California" }
   },
   {
      "name": "Bob",
      "gpa": 3.2,
      "location": { city: "Albany", state: "New York" }
   }
] )

Procedures

The following examples show you how to:

Create an Index on a Single Field
Create an Index on an Embedded Field

Create an Index on a Single Field

Consider a school administrator who frequently looks up students by their GPA. You can create an index on the gpa field to improve performance for those queries:

db.students.createIndex( { gpa: 1 } )

Results

The index supports queries that select on the field gpa, such as the following:

db.students.find( { gpa: 3.6 } )
db.students.find( { gpa: { $lt: 3.4 } } )

Create an Index on an Embedded Field

You can create indexes on fields within embedded documents. Indexes on embedded fields can fulfill queries that use dot notation.

The location field is an embedded document that contains the embedded fields city and state. Create an index on the location.state field:

db.students.createIndex( { "location.state": 1 } )

Results

The index supports queries on the field location.state, such as the following:

db.students.find( { "location.state": "California" } )
db.students.find( { "location.city": "Albany", "location.state": "New York" } )

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Single Field

Embedded Documents