Index direction (ascending vs descending) in MongoDB - Practice Questions

Challenge - 5 Problems

❓ query_result

intermediate

Effect of ascending index on query sort

Given a MongoDB collection products with an ascending index on price, what will be the order of price values returned by this query?

db.products.find().sort({price: 1})

A Documents sorted by price from lowest to highest

B Documents sorted by price from highest to lowest

C Documents returned in insertion order

D Documents sorted randomly

💡 Hint

Ascending index means sorting from smallest to largest.

An ascending index on price stores values from lowest to highest. Sorting with {price: 1} uses this index to return documents in ascending order.

❓ query_result

intermediate

Effect of descending index on query sort

Given a MongoDB collection orders with a descending index on orderDate, what will be the order of orderDate values returned by this query?

db.orders.find().sort({orderDate: -1})

A Documents sorted by orderDate ascending

B Documents sorted by orderDate from oldest to newest

C Documents returned in random order

D Documents sorted by orderDate from newest to oldest

💡 Hint

Descending index means sorting from largest to smallest.

A descending index on orderDate stores values from newest to oldest. Sorting with {orderDate: -1} uses this index to return documents in descending order.

🧠 Conceptual

advanced

Index direction impact on compound index queries

Consider a compound index on {category: 1, price: -1} in a MongoDB collection. Which query will benefit most from this index?

A db.items.find().sort({category: -1, price: 1})

B db.items.find({category: 'books'}).sort({category: 1, price: -1})

C db.items.find({price: {$gt: 10}}).sort({price: -1})

D db.items.find({category: 'books'}).sort({price: 1})

💡 Hint

The query must match the index fields and directions to use the index efficiently.

The compound index {category: 1, price: -1} supports queries filtering by category and sorting by price descending. Option B matches both fields and directions.

📝 Syntax

advanced

Correct syntax for creating descending index

Which of the following commands correctly creates a descending index on the score field in MongoDB?

A db.scores.createIndex({score: 0})

B db.scores.createIndex({score: 'desc'})

C db.scores.createIndex({score: -1})

D db.scores.createIndex({score: 'descending'})

💡 Hint

Index direction is specified by 1 for ascending or -1 for descending.

The correct syntax uses -1 to specify descending order. Other strings or zero are invalid.

❓ optimization

expert

Choosing index direction for frequent queries

You have a MongoDB collection events with frequent queries sorting by timestamp ascending and some queries sorting by timestamp descending. Which index direction should you choose to optimize overall performance?

A Create an ascending index on timestamp to optimize ascending sorts; descending sorts will scan backward

B Create a descending index on timestamp to optimize descending sorts; ascending sorts will scan backward

C Create two separate indexes: one ascending and one descending on timestamp

D Create a hashed index on timestamp for both ascending and descending sorts

💡 Hint

MongoDB can scan indexes backward to support opposite sort direction.

Creating an ascending index allows efficient ascending sorts and MongoDB can scan it backward for descending sorts, avoiding extra index creation.