sort method ascending and descending in MongoDB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Sort documents by age ascending

Given a collection users with documents containing name and age, what is the output of this query?

db.users.find().sort({age: 1})

Assume the collection has:
{name: 'Alice', age: 30}
{name: 'Bob', age: 25}
{name: 'Carol', age: 35}

MongoDB

db.users.find().sort({age: 1})

A [{name: 'Bob', age: 25}, {name: 'Alice', age: 30}, {name: 'Carol', age: 35}]

B [{name: 'Carol', age: 35}, {name: 'Alice', age: 30}, {name: 'Bob', age: 25}]

C [{name: 'Alice', age: 30}, {name: 'Bob', age: 25}, {name: 'Carol', age: 35}]

D [{name: 'Bob', age: 25}, {name: 'Carol', age: 35}, {name: 'Alice', age: 30}]

💡 Hint

Sorting by age with 1 means ascending order.

The sort method with {age: 1} sorts documents by age from smallest to largest.

❓ query_result

intermediate

Sort documents by age descending

Using the same users collection, what is the output of this query?

db.users.find().sort({age: -1})

With documents:
{name: 'Alice', age: 30}
{name: 'Bob', age: 25}
{name: 'Carol', age: 35}

MongoDB

db.users.find().sort({age: -1})

A [{name: 'Bob', age: 25}, {name: 'Alice', age: 30}, {name: 'Carol', age: 35}]

B [{name: 'Alice', age: 30}, {name: 'Carol', age: 35}, {name: 'Bob', age: 25}]

C [{name: 'Carol', age: 35}, {name: 'Bob', age: 25}, {name: 'Alice', age: 30}]

D [{name: 'Carol', age: 35}, {name: 'Alice', age: 30}, {name: 'Bob', age: 25}]

💡 Hint

Sorting by age with -1 means descending order.

The sort method with {age: -1} sorts documents by age from largest to smallest.

🧠 Conceptual

advanced

Understanding sort order values

In MongoDB, what do the values 1 and -1 mean when used in the sort() method?

A 1 means ascending order, -1 means descending order

B 1 means descending order, -1 means ascending order

C 1 means sort by string length, -1 means sort by numeric value

D 1 means no sorting, -1 means reverse sorting

💡 Hint

Think about smallest to largest and largest to smallest.

In MongoDB, 1 sorts ascending (smallest to largest), -1 sorts descending (largest to smallest).

📝 Syntax

advanced

Identify the invalid sort syntax

Which of the following MongoDB sort method calls will cause a syntax error?

A db.collection.find().sort({age: 1})

B db.collection.find().sort({age: -1})

C db.collection.find().sort({age: 'asc'})

D db.collection.find().sort({age: 0})

💡 Hint

Sort values must be numeric 1 or -1.

MongoDB sort values must be 1 or -1. Using 'asc' as a string causes an error.

❓ optimization

expert

Optimizing sort with index

You have a large MongoDB collection with an index on age. Which query will use the index efficiently for sorting by age descending?

A db.collection.find().sort({age: 0})

B db.collection.find().sort({age: -1})

C db.collection.find().sort({name: 1})

D db.collection.find().sort({age: 1})

💡 Hint

Index on age supports sorting by age ascending or descending.

Sorting by age descending matches the index on age and uses it efficiently.

Practice

1. What does the sort({ age: 1 }) method do in MongoDB?

easy

A. Deletes documents with age less than 1

B. Sorts documents by age in descending order (largest to smallest)

C. Filters documents where age equals 1

D. Sorts documents by age in ascending order (smallest to largest)

Solution

1. Step 1: Understand the sort method parameter

   The number 1 in sort({ age: 1 }) means ascending order.

2. Step 2: Interpret the sorting effect

   Documents will be arranged from smallest age to largest age.

3. Final Answer:

   Sorts documents by age in ascending order (smallest to largest) -> Option D

4. Quick Check:

   sort({ field: 1 }) = ascending order [OK]

Hint: 1 means ascending order, -1 means descending order [OK]

Common Mistakes:

• Confusing 1 with descending order
• Thinking sort filters data
• Assuming sort deletes documents

2. Which of the following is the correct syntax to sort documents by score in descending order in MongoDB?

easy

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

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

C. db.collection.find().sort(score: -1)

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

Solution

1. Step 1: Check the correct object syntax for sort

   The sort method requires an object with field name as key and 1 or -1 as value, inside curly braces.

2. Step 2: Identify descending order syntax

   Descending order is indicated by -1, so { score: -1 } is correct.

3. Final Answer:

   db.collection.find().sort({ score: -1 }) -> Option A

4. Quick Check:

   sort({ field: -1 }) = descending order [OK]

Hint: Use curly braces and colon: sort({ field: -1 }) [OK]

Common Mistakes:

• Missing curly braces around sort argument
• Using parentheses instead of braces
• Putting -1 as key instead of value

3. Given the documents: [{"name": "Anna", "score": 85}, {"name": "Ben", "score": 92}, {"name": "Cara", "score": 78}], what will be the order of names after running db.students.find().sort({ score: 1 })?

medium

A. ["Ben", "Anna", "Cara"]

B. ["Cara", "Ben", "Anna"]

C. ["Cara", "Anna", "Ben"]

D. ["Anna", "Cara", "Ben"]

Solution

1. Step 1: Understand ascending sort by score

   Sorting by score ascending means from smallest to largest score: 78, 85, 92.

2. Step 2: Map scores to names in order

   78 = Cara, 85 = Anna, 92 = Ben, so order is ["Cara", "Anna", "Ben"].

3. Final Answer:

   ["Cara", "Anna", "Ben"] -> Option C

4. Quick Check:

   sort({ score: 1 }) = ascending order [OK]

Hint: Ascending sort orders from smallest to largest [OK]

Common Mistakes:

• Mixing ascending with descending order
• Sorting by name instead of score
• Confusing array order in output

4. What is wrong with this MongoDB query?

db.products.find().sort({ price: 2 })

medium

A. The find() method cannot be chained with sort()

B. The sort value must be 1 or -1, not 2

C. The field name 'price' is invalid

D. Missing parentheses after sort

Solution

1. Step 1: Check valid sort values

   MongoDB sort only accepts 1 for ascending or -1 for descending, not 2.

2. Step 2: Identify the error cause

   Using 2 will cause a syntax or runtime error because it's invalid.

3. Final Answer:

   The sort value must be 1 or -1, not 2 -> Option B

4. Quick Check:

   sort values = 1 or -1 only [OK]

Hint: Sort values must be exactly 1 or -1 [OK]

Common Mistakes:

• Using numbers other than 1 or -1
• Assuming any positive number works
• Thinking sort can't chain after find()

5. You have a collection with documents containing category and price. How do you sort first by category ascending, then by price descending?

hard

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

B. db.collection.find().sort({ price: -1, category: 1 })

C. db.collection.find().sort({ category: -1, price: 1 })

D. db.collection.find().sort({ category: 1 }).sort({ price: -1 })

Solution

1. Step 1: Understand multi-field sort syntax

   MongoDB sorts by fields in the order they appear in the object passed to sort().

2. Step 2: Apply ascending to category and descending to price

   Use { category: 1, price: -1 } to sort category ascending, then price descending within each category.

3. Final Answer:

   db.collection.find().sort({ category: 1, price: -1 }) -> Option A

4. Quick Check:

   Multi-field sort = object with fields in order [OK]

Hint: List fields in sort object in desired priority order [OK]

Common Mistakes:

• Reversing field order changes sort priority
• Trying to chain multiple sort() calls
• Using wrong sort values for fields