$limit and $skip stages in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the $limit stage do in a MongoDB aggregation pipeline?

The $limit stage restricts the number of documents passed to the next stage. It returns only the first N documents, where N is the specified limit number.

beginner

What is the purpose of the $skip stage in MongoDB aggregation?

The $skip stage skips over a specified number of documents and passes the remaining documents to the next stage. It is often used to paginate results.

intermediate

How do $skip and $limit work together in MongoDB?

You can use $skip to jump past a number of documents and then $limit to restrict how many documents to return after skipping. This combination is useful for pagination.

beginner

If you want to get the first 5 documents from a collection using aggregation, which stage would you use?

Use the $limit stage with the value 5 to get the first 5 documents.

intermediate

What happens if you use $skip with a number larger than the total documents in the collection?

If $skip is larger than the total documents, the result will be an empty set because all documents are skipped.

Which MongoDB aggregation stage limits the number of documents passed to the next stage?

A $match

B $skip

C $limit

D $group

$limit restricts the number of documents passed forward.

What does the $skip stage do in an aggregation pipeline?

A Limits the number of documents

B Groups documents by a field

C Sorts the documents

D Skips a specified number of documents

$skip skips over a number of documents before passing the rest.

To get documents 11 to 20 from a collection, which combination of stages is correct?

A <code>$skip: 10</code> then <code>$limit: 10</code>

B <code>$limit: 10</code> then <code>$skip: 10</code>

C <code>$limit: 20</code> then <code>$skip: 10</code>

D <code>$skip: 20</code> then <code>$limit: 10</code>

First skip 10 documents, then limit to 10 documents to get 11-20.

What will be the output if $skip is set to 0?

A All documents are skipped

B No documents are skipped

C Only one document is skipped

D Error occurs

$skip: 0 means no documents are skipped.

Which stage should come first to paginate results correctly?

A <code>$skip</code> then <code>$limit</code>

B Order does not matter

C <code>$limit</code> then <code>$skip</code>

D Use only <code>$limit</code>

You skip first, then limit the number of documents returned.

Explain how you would use $skip and $limit to get the second page of results if each page shows 10 documents.

Think about how many documents to skip to start the second page.

What happens if you use $limit without $skip in a query?

Consider what limiting alone does to the result set.

Practice

1. What does the $limit stage do in a MongoDB aggregation pipeline?

easy

A. It skips a number of documents before returning results.

B. It groups documents by a specified field.

C. It sorts the documents in ascending order.

D. It restricts the number of documents returned.

Solution

1. Step 1: Understand the purpose of $limit

   The $limit stage restricts the number of documents that pass through the pipeline to a specified count.

2. Step 2: Compare with other stages

   $skip skips documents, $sort orders them, and $group groups them. Only $limit restricts count.

3. Final Answer:

   It restricts the number of documents returned. -> Option D

4. Quick Check:

   $limit = restrict count [OK]

Hint: Remember: limit = how many results you get [OK]

Common Mistakes:

• Confusing $limit with $skip
• Thinking $limit sorts data
• Mixing $limit with $group

2. Which of the following is the correct syntax to skip 5 documents and then limit the result to 10 documents in a MongoDB aggregation pipeline?

easy

A. [{ $skip: 5 }, { $limit: 10 }]

B. [{ $limit: 10 }, { $skip: 5 }]

C. [{ $skip: 10 }, { $limit: 5 }]

D. [{ $limit: 5 }, { $skip: 10 }]

Solution

1. Step 1: Identify correct order of stages

   To skip first, use $skip then limit results with $limit.

2. Step 2: Match syntax with values

   Skipping 5 then limiting to 10 matches [{ $skip: 5 }, { $limit: 10 }].

3. Final Answer:

   [{ $skip: 5 }, { $limit: 10 }] -> Option A

4. Quick Check:

   Skip first, then limit [OK]

Hint: Skip first, then limit for paging [OK]

Common Mistakes:

• Reversing $limit and $skip order
• Using wrong numbers for skip and limit
• Confusing syntax with find() options

3. Given a collection with documents numbered 1 to 10, what will be the output of this aggregation pipeline?

[{ $skip: 3 }, { $limit: 4 }]

medium

A. [1, 2, 3, 4]

B. [4, 5, 6, 7]

C. [3, 4, 5, 6]

D. [5, 6, 7, 8]

Solution

1. Step 1: Apply $skip: 3 on documents 1 to 10

   Skipping 3 documents removes 1, 2, 3; remaining are 4 to 10.

2. Step 2: Apply $limit: 4 on remaining documents

   Limit to 4 documents returns 4, 5, 6, 7.

3. Final Answer:

   [4, 5, 6, 7] -> Option B

4. Quick Check:

   Skip 3, then take 4 [OK]

Hint: Skip removes first N, limit picks next M [OK]

Common Mistakes:

• Counting skip as inclusive
• Mixing skip and limit values
• Assuming skip resets numbering

4. You wrote this aggregation pipeline but it returns only 2 documents instead of skipping the first 3 from the full collection and limiting to 5:

[{ $limit: 5 }, { $skip: 3 }]

What is the problem?

medium

A. You need to use find() instead of aggregation for skip and limit.

B. The syntax is invalid; $skip cannot be used in aggregation.

C. $skip must come before $limit to work correctly.

D. The pipeline is missing a $match stage before $limit.

Solution

1. Step 1: Understand stage order effect

   $limit first restricts to 5 documents, then $skip tries to skip 3 from those 5.

2. Step 2: Why it returns only 2 documents

   Because $skip after $limit skips from a smaller set (first 5), not the full collection.

3. Final Answer:

   $skip must come before $limit to work correctly. -> Option C

4. Quick Check:

   Skip first, then limit [OK]

Hint: Order matters: skip before limit [OK]

Common Mistakes:

• Placing $limit before $skip
• Thinking $skip is invalid in aggregation
• Confusing aggregation with find()

5. You want to implement pagination on a collection with 100 documents, showing 10 documents per page. Which aggregation pipeline correctly gets the 3rd page of results?

hard

A. [{ $skip: 20 }, { $limit: 10 }]

B. [{ $skip: 30 }, { $limit: 10 }]

C. [{ $limit: 10 }, { $skip: 20 }]

D. [{ $limit: 30 }, { $skip: 10 }]

Solution

1. Step 1: Calculate skip value for page 3

   Each page shows 10 documents, so page 3 skips 2 pages x 10 = 20 documents.

2. Step 2: Apply skip and limit in correct order

   Skip 20 documents, then limit to 10 documents to get page 3 results.

3. Final Answer:

   [{ $skip: 20 }, { $limit: 10 }] -> Option A

4. Quick Check:

   Skip (page-1)*size, then limit size [OK]

Hint: Skip (page-1)*size, then limit size [OK]

Common Mistakes:

• Using wrong skip calculation
• Reversing skip and limit order
• Confusing page number with skip count