limit method for pagination in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What documents are returned by this MongoDB query?

Consider a collection books with documents sorted by publishedYear ascending. What documents will this query return?

db.books.find().sort({publishedYear: 1}).limit(3)

MongoDB

db.books.find().sort({publishedYear: 1}).limit(3)

A The first 3 books with the earliest publishedYear values.

B The last 3 books with the latest publishedYear values.

C All books sorted by publishedYear, but only those with publishedYear less than 3.

D 3 random books from the collection.

💡 Hint

Remember, limit(n) returns only the first n documents after sorting.

The query sorts all books by publishedYear ascending (earliest first), then limits the output to the first 3 documents in that order.

❓ query_result

intermediate

What is the output of this MongoDB query with skip and limit?

Given a collection users sorted by age ascending, what documents does this query return?

db.users.find().sort({age: 1}).skip(5).limit(4)

MongoDB

db.users.find().sort({age: 1}).skip(5).limit(4)

A Users ranked 1st to 4th youngest by age.

B Users ranked 6th to 9th youngest by age.

C Users ranked 5th to 8th youngest by age.

D Users ranked 5th to 9th youngest by age.

💡 Hint

Skip removes the first 5 documents, then limit returns the next 4.

The query skips the first 5 users (youngest 5), then returns the next 4 users sorted by age ascending, which are users ranked 6th to 9th youngest.

📝 Syntax

advanced

Which MongoDB query correctly limits results to 10 documents after sorting by score descending?

Choose the query that correctly returns the top 10 documents sorted by score descending.

A db.collection.find().limit(10).sort({score: -1})

B db.collection.find().sort({score: 1}).limit(10)

C db.collection.find().limit(10).sort({score: 1})

D db.collection.find().sort({score: -1}).limit(10)

💡 Hint

Sorting must happen before limiting to get the top scores.

The correct order is to sort first by score descending, then limit to 10 documents. Option D does this correctly.

❓ optimization

advanced

How to optimize pagination for large collections using limit and skip?

You want to paginate through a large MongoDB collection efficiently. Which approach is best to avoid performance issues with skip and limit?

A Use <code>limit</code> only without <code>skip</code> to get the first page repeatedly.

B Use <code>skip</code> with <code>limit</code> but add <code>sort</code> on a non-indexed field.

C Use a range query on an indexed field (like _id) with <code>limit</code> instead of large skips.

D Use <code>skip</code> with large offsets and <code>limit</code> as usual.

💡 Hint

Large skips cause MongoDB to scan many documents internally.

Using range queries on indexed fields avoids scanning skipped documents, improving pagination performance.

🧠 Conceptual

expert

Why does using only limit without sort cause inconsistent pagination results?

In MongoDB, if you paginate using only limit without specifying sort, what problem can occur?

A Documents may appear in different orders on different queries, causing inconsistent pages.

B The query will always return the same documents regardless of changes in the collection.

C MongoDB will throw a syntax error because <code>limit</code> requires <code>sort</code>.

D The query will return documents sorted by _id automatically, so pagination is stable.

💡 Hint

Without sorting, MongoDB does not guarantee order of documents returned.

Without a sort, the order of documents returned is not guaranteed and can change, leading to inconsistent pagination results.