Question

You can combine the ________ constraint with the sparse index to filter these null values from the unique index and avoid the error.

(a) Hashed

(b) Unique

(c) Sparse

(d) Compound

I had been asked this question in a job interview.

My query is from Index Properties in chapter Index/Indexing Concepts of MongoDB

Answer 1

Correct option is (c) Sparse

To explain I would say: If a document does not have a value for the indexed field in a unique index, the index will store a null value for this document.