Question

Point out the wrong statement.

(a) The unique constraint applies to separate documents in the collection

(b) Unique index prevents separate documents from having the same value for the indexed key

(c) Index does prevent a document from having multiple elements or embedded documents in an indexed array from having the same value

(d) None of the mentioned

The question was asked in quiz.

I would like to ask this question from Index Properties topic in portion Index/Indexing Concepts of MongoDB

Answer 1

The correct answer is (c) Index does prevent a document from having multiple elements or embedded documents in an indexed array from having the same value

Best explanation: In the case of a single document with repeating values, the repeated value is inserted into the index only once.