In MongoDB a collection has a compound index {a:1,b:-1}. A query db.c.find({a:{$gt:3},b:{$lt:7}}).sort({a:1,b:-1}) is executed. Which of the following describes the index intersection plan and its sorting behaviour?
Correct: N/A
The index is a prefix match for both predicates and the sort order aligns exactly with the index direction. MongoDB can traverse the index range (3, +∞) for a and (-∞, 7) for b, producing already ordered documents, so no additional sort stage is needed; the query is covered by the index.