Sorting results in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output order of this Elasticsearch sort query?

Given the following Elasticsearch query, what is the order of the returned documents by their price field?

Elasticsearch

{
  "query": { "match_all": {} },
  "sort": [
    { "price": { "order": "asc" } }
  ]
}

A Documents sorted from lowest to highest price

B Documents sorted from highest to lowest price

C Documents sorted alphabetically by price field

D Documents returned in random order

💡 Hint

Look at the order value inside the sort array.

The sort clause with order": "asc" sorts documents from the lowest to the highest value of the price field.

❓ Predict Output

intermediate

What happens if you sort by a non-existent field in Elasticsearch?

Consider this Elasticsearch query that sorts by a field rating which does not exist in any document. What will be the result?

Elasticsearch

{
  "query": { "match_all": {} },
  "sort": [
    { "rating": { "order": "desc" } }
  ]
}

A Elasticsearch throws an error about missing field

B Documents are returned in original order because <code>rating</code> is missing

C Documents are sorted with missing <code>rating</code> treated as highest values

D Documents are sorted with missing <code>rating</code> treated as lowest values

💡 Hint

By default ('_last'), missing fields are treated as highest values.

Elasticsearch's default for missing sort values is '_last', treating them as higher than any existing value. For desc order, documents missing rating appear last.

🔧 Debug

advanced

Why does this Elasticsearch sort query cause an error?

Look at this Elasticsearch query that tries to sort by date descending but causes an error. What is the cause?

Elasticsearch

{
  "query": { "match_all": {} },
  "sort": [
    { "date": "desc" }
  ]
}

A The <code>desc</code> value must be uppercase

B The <code>date</code> field does not exist in the index

C Sorting by date requires a script, not a field name

D The sort syntax is invalid; the order must be inside an object with key <code>order</code>

💡 Hint

Check the correct syntax for sorting by a field with order.

The correct syntax for sorting by a field with order is to use an object with the key order. Writing { "date": "desc" } is invalid. It should be { "date": { "order": "desc" } }.

🧠 Conceptual

advanced

How does Elasticsearch handle sorting by multiple fields?

Given this sort clause, how does Elasticsearch order the documents?

{
  "sort": [
    { "price": { "order": "asc" } },
    { "rating": { "order": "desc" } }
  ]
}

A Documents are sorted first by <code>price</code> ascending, then by <code>rating</code> descending for ties

B Documents are sorted by <code>rating</code> descending, then by <code>price</code> ascending

C Documents are sorted randomly ignoring the fields

D Documents are sorted by the sum of <code>price</code> and <code>rating</code>

💡 Hint

Think about the order of fields in the sort array.

Elasticsearch sorts documents by the first field in the sort array. If there are ties, it uses the next field to break ties, and so on. Here, it sorts by price ascending first, then by rating descending.

❓ Predict Output

expert

What is the output of this Elasticsearch sort with nested field and missing values?

Consider documents with a nested field author.name. This query sorts by author.name.keyword ascending, treating missing values as last. What is the order of documents?

Elasticsearch

{
  "query": { "match_all": {} },
  "sort": [
    {
      "author.name.keyword": {
        "order": "asc",
        "missing": "_last"
      }
    }
  ]
}

A Documents with missing <code>author.name.keyword</code> appear first, others sorted Z to A

B Documents with <code>author.name.keyword</code> missing appear at the end, others sorted A to Z

C Documents are sorted by <code>author.name.keyword</code> descending ignoring missing

D Elasticsearch throws an error because <code>missing</code> is not a valid parameter

💡 Hint

Check the missing parameter usage in sorting.

The missing": "_last" option tells Elasticsearch to put documents missing the field at the end of the sorted list. The order": "asc" sorts the existing values alphabetically from A to Z.

Practice

1. What does the sort parameter do in an Elasticsearch query?

easy

A. It arranges the search results in a specified order.

B. It filters the search results based on a condition.

C. It changes the index mapping settings.

D. It deletes documents from the index.

Solution

1. Step 1: Understand the purpose of sort

   The sort parameter is used to order search results by a field in ascending or descending order.

2. Step 2: Differentiate from other parameters

   Filtering narrows results, mapping changes structure, and deleting removes data, none of which are sorting.

3. Final Answer:

   It arranges the search results in a specified order. -> Option A

4. Quick Check:

   Sorting = arranging results [OK]

Hint: Sort means order your results by a field [OK]

Common Mistakes:

• Confusing sorting with filtering
• Thinking sort deletes or changes data
• Mixing sort with index settings

2. Which of the following is the correct syntax to sort results by the field price in descending order?

easy

A. "sort": [{"price": "desc"}]

B. "sort": {"price": "descending"}

C. "sort": ["price:desc"]

D. "sort": [{"price": "down"}]

Solution

1. Step 1: Check Elasticsearch sort syntax

   Sorting uses an array of objects with field name and order as "asc" or "desc" strings.

2. Step 2: Validate each option

   "sort": [{"price": "desc"}] uses correct JSON array and "desc" keyword. Others use invalid keywords or formats.

3. Final Answer:

   "sort": [{"price": "desc"}] -> Option A

4. Quick Check:

   Correct syntax uses array and "desc" [OK]

Hint: Use array with field and "asc" or "desc" strings [OK]

Common Mistakes:

• Using wrong keywords like "descending" or "down"
• Not using an array for sort
• Incorrect JSON object structure

3. Given this Elasticsearch query snippet, what is the order of the returned documents by age?

{
  "sort": [{"age": "asc"}]
}

medium

A. Documents are sorted from oldest to youngest.

B. Documents are sorted alphabetically by age.

C. Documents are sorted randomly.

D. Documents are sorted from youngest to oldest.

Solution

1. Step 1: Understand the meaning of "asc" in sorting

   "asc" means ascending order, so smaller values come first.

2. Step 2: Apply to the field "age"

   Sorting by age ascending means documents with lower age values appear before higher ones.

3. Final Answer:

   Documents are sorted from youngest to oldest. -> Option D

4. Quick Check:

   "asc" = ascending = smallest to largest [OK]

Hint: "asc" means smallest to largest values [OK]

Common Mistakes:

• Confusing "asc" with descending order
• Thinking sorting is random
• Assuming alphabetical sort on numbers

4. Identify the error in this Elasticsearch sort snippet:

{
  "sort": {"date": "asc"}
}

medium

A. Sort cannot be used with date fields.

B. Sort must be an array, not a single object.

C. Field name "date" must be inside quotes.

D. The order "asc" is invalid; should be "ascending".

Solution

1. Step 1: Check the required structure for sort

   Sort expects an array of objects, even if sorting by one field.

2. Step 2: Analyze the given snippet

   The snippet uses an object directly, missing the array brackets [].

3. Final Answer:

   Sort must be an array, not a single object. -> Option B

4. Quick Check:

   Sort = array of objects [OK]

Hint: Sort always uses an array, even for one field [OK]

Common Mistakes:

• Using object instead of array for sort
• Wrong order keywords like "ascending"
• Thinking sort can't be used on dates

5. You want to sort search results first by category alphabetically ascending, then by price descending. Which is the correct sort clause?

hard

A. "sort": {"category": "asc", "price": "desc"}

B. "sort": [{"price": "desc"}, {"category": "asc"}]

C. "sort": [{"category": "asc"}, {"price": "desc"}]

D. "sort": [{"category": "desc"}, {"price": "asc"}]

Solution

1. Step 1: Understand multi-level sorting order

   Sorting applies fields in order: first field sorts primary, second field breaks ties.

2. Step 2: Match required order

   First by category ascending, then by price descending means category asc first, price desc second.

3. Step 3: Validate syntax

   Sort must be an array of objects with field and order pairs.

4. Final Answer:

   "sort": [{"category": "asc"}, {"price": "desc"}] -> Option C

5. Quick Check:

   Primary asc category, secondary desc price [OK]

Hint: List sort fields in order inside array [OK]

Common Mistakes:

• Reversing sort order of fields
• Using object instead of array for multiple fields
• Mixing ascending and descending incorrectly