$limit and $skip stages in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to limit the results to 5 documents.

MongoDB

db.collection.aggregate([{ $limit: [1] }])

Drag options to blanks, or click blank then click option'

A5

B1

C0

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 will return no documents.

Using a number larger than the collection size returns all documents.

The $limit stage restricts the number of documents passed to the next stage. Using 5 returns only the first 5 documents.

2fill in blank

medium

Complete the code to skip the first 3 documents in the aggregation.

MongoDB

db.collection.aggregate([{ $skip: [1] }])

Drag options to blanks, or click blank then click option'

A0

B1

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 means no documents are skipped.

Using a number larger than the collection size returns no documents.

The $skip stage skips the first N documents. Using 3 skips the first three documents and returns the rest.

3fill in blank

hard

Fix the error in the aggregation pipeline to correctly skip 2 documents.

MongoDB

db.collection.aggregate([{ $skip: [1] }])

Drag options to blanks, or click blank then click option'

A'2'

B2

C-2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers causes type errors.

Negative skip values are invalid.

The $skip stage requires a non-negative integer. Using the number 2 correctly skips two documents. Using a string or negative number causes errors.

4fill in blank

hard

Fill both blanks to skip the first 4 documents and then limit the results to 3 documents.

MongoDB

db.collection.aggregate([{ $skip: [1] }, { $limit: [2] }])

Drag options to blanks, or click blank then click option'

A4

B3

C5

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the numbers will change the output.

Using numbers too large may return no documents.

First, $skip: 4 skips the first four documents. Then, $limit: 3 limits the output to the next three documents.

5fill in blank

hard

Fill all three blanks to skip 2 documents, limit to 4 documents, and then skip 1 more document.

MongoDB

db.collection.aggregate([{ $skip: [1] }, { $limit: [2] }, { $skip: [3] }])

Drag options to blanks, or click blank then click option'

A2

B4

C1

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing the order of stages changes the result.

Using wrong numbers can return unexpected documents.

The pipeline first skips 2 documents, then limits the output to 4 documents, and finally skips 1 document from those 4, resulting in documents 4 to 6 from the original collection.

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