Download Full Version C100DBA MongoDB Exam

The query contains equality predicates on both city and occupation, so an efficient compound index should contain both fields. Options A and C include only one query predicate plus the unrelated name field, forcing MongoDB to perform additional filtering that the index cannot resolve. Options B and D both contain the complete predicate set. For a query consisting entirely of equality predicates, MongoDB does not require those equality keys to appear in a particular order relative to one another for the query itself; { city: 1, occupation: 1 } and { occupation: 1, city: 1 } can both support the two equality conditions effectively. The original question appears to expect B because it mirrors the field order used in the query, but that distinction is not technically required under MongoDB ' s equality-key guidance. Field order becomes much more significant when the workload also needs a particular index prefix, sort order, range predicate, or when one ordering better supports additional common queries. Accordingly, the technically accurate review result is B and D, with B being the likely intended exam choice.

Study Guide reference/topic:Indexing and Query Optimization - compound indexes, equality predicates, and index key ordering.

===========