Sparse indexes in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a sparse index in MongoDB?

A sparse index only includes documents in the index if the indexed field exists. Documents without the field are not indexed.

beginner

How does a sparse index differ from a regular index?

A regular index includes all documents, even if the indexed field is missing or null. A sparse index skips documents missing the field.

intermediate

Why use a sparse index?

To save space and improve performance when many documents do not have the indexed field, because only documents with the field are indexed.

intermediate

Can a sparse index be used with unique constraints?

Yes, but only documents with the indexed field are checked for uniqueness. Documents without the field can have duplicates.

beginner

How do you create a sparse index in MongoDB?

Use the createIndex method with the option { sparse: true }, for example: db.collection.createIndex({ field: 1 }, { sparse: true })

What does a sparse index in MongoDB exclude?

A All documents in the collection

B Documents where the indexed field is present

C Documents where the indexed field is missing

D Only documents with null values in the indexed field

Sparse indexes exclude documents where the indexed field does not exist.

Which option is used to create a sparse index in MongoDB?

A { unique: true }

B { sparse: true }

C { background: true }

D { expireAfterSeconds: 3600 }

The option { sparse: true } tells MongoDB to create a sparse index.

Can a sparse index enforce uniqueness on documents missing the indexed field?

A Yes, it enforces uniqueness on all documents

B Yes, but only if the field is null

C No, sparse indexes cannot be unique

D No, it only enforces uniqueness on documents with the indexed field

Sparse unique indexes enforce uniqueness only on documents that have the indexed field.

What is a benefit of using a sparse index?

A Saves space by indexing fewer documents

B Indexes all documents regardless of field presence

C Automatically updates documents

D Prevents all duplicates in the collection

Sparse indexes save space by indexing only documents that contain the indexed field.

If a document does not have the indexed field, how does a sparse index treat it?

A Excludes it from the index

B Throws an error

C Indexes it as zero

D Includes it in the index with a null value

Documents missing the indexed field are excluded from a sparse index.

Explain what a sparse index is and when you would use it in MongoDB.

Think about indexing only documents that have a certain field.

Describe how uniqueness works with sparse indexes in MongoDB.

Consider how missing fields affect unique constraints.