Constant score query in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this constant_score query?

Given the following Elasticsearch query, what is the score of each document matching the filter?

Elasticsearch

{
  "query": {
    "constant_score": {
      "filter": {
        "term": { "status": "active" }
      },
      "boost": 5
    }
  }
}

A Each matching document has a score of 5

B Each matching document has a score equal to the term frequency of "active"

C Each matching document has a score of 1

D Each matching document has a score of 0

💡 Hint

Remember that constant_score sets the score to the boost value for all matching documents.

The constant_score query wraps a filter and assigns a fixed score (boost) to all documents matching the filter, ignoring relevance scoring.

🧠 Conceptual

intermediate

Why use a constant_score query instead of a match query?

Which of the following is the main reason to use a constant_score query?

A To perform full-text search with relevance scoring

B To sort documents by their field values

C To assign the same score to all matching documents regardless of relevance

D To update documents in the index

💡 Hint

Think about when you want to ignore relevance and just filter with a fixed score.

Constant_score queries are used when you want to filter documents and assign them a fixed score, ignoring the usual relevance calculations.

🔧 Debug

advanced

Identify the error in this constant_score query

What error will this query produce?

Elasticsearch

{
  "query": {
    "constant_score": {
      "filter": {
        "match": { "title": "Elasticsearch" }
      },
      "boost": "high"
    }
  }
}

A SyntaxError: missing comma after filter

B TypeError: boost must be a number, not a string

C No error, query runs successfully

D RuntimeError: match query not allowed inside constant_score

💡 Hint

Check the type of the boost value.

The boost parameter must be a numeric value. Using a string like "high" causes a type error.

📝 Syntax

advanced

Which option is the correct syntax for a constant_score query with a range filter?

Select the valid constant_score query that filters documents with age greater than 30 and assigns a boost of 3.

A { "query": { "constant_score": { "filter": { "range": { "age": { "greater_than": 30 } } }, "boost": 3 } } }

B { "query": { "constant_score": { "filter": { "range": { "age": { "min": 30 } } }, "boost": 3 } } }

C { "query": { "constant_score": { "filter": { "range": { "age": { "gte": 30 } } }, "boost": 3 } } }

D { "query": { "constant_score": { "filter": { "range": { "age": { "gt": 30 } } }, "boost": 3 } } }

💡 Hint

Check the correct range operator for greater than in Elasticsearch.

Elasticsearch range query uses 'gt' for greater than (strictly > 30) and 'gte' for greater than or equal to (>= 30). The question specifies 'greater than 30', so 'gt' (option D) is correct. Option D uses invalid 'min', option D uses invalid 'greater_than', option D uses 'gte' which includes 30.

🚀 Application

expert

How many documents will be scored with boost 10 in this query?

Assume the index has 1000 documents. 200 have field "category" equal to "books". What is the number of documents that will have a score of 10 after running this query?

Elasticsearch

{
  "query": {
    "constant_score": {
      "filter": {
        "term": { "category": "books" }
      },
      "boost": 10
    }
  }
}

A 200

B 1000

C 0

D 800

💡 Hint

Only documents matching the filter get the boost score.

Only the 200 documents with category 'books' match the filter and get the constant score of 10. Others are excluded.

Practice

1. What is the main purpose of a constant_score query in Elasticsearch?

easy

A. To filter documents and assign the same score to all matched documents

B. To sort documents by their relevance score

C. To perform a full-text search with varying scores

D. To aggregate documents by a field value

Solution

1. Step 1: Understand the role of constant_score query

   The constant_score query filters documents and assigns the same score to all matches, ignoring relevance scoring.

2. Step 2: Compare with other query types

   Unlike full-text queries that score by relevance, constant_score keeps scores equal for filtered documents.

3. Final Answer:

   To filter documents and assign the same score to all matched documents -> Option A

4. Quick Check:

   constant_score = equal scoring for filtered docs [OK]

Hint: Constant score means all matched docs get the same score [OK]

Common Mistakes:

• Thinking it sorts by relevance
• Confusing with full-text scoring
• Assuming it aggregates data

2. Which of the following is the correct syntax to create a constant score query with a filter on field status equal to active?

easy

A. {"constant_score": {"filter": {"match": {"status": "active"}}}}

B. {"constant_score": {"query": {"term": {"status": "active"}}}}

C. {"constant_score": {"term": {"status": "active"}}}

D. {"constant_score": {"filter": {"term": {"status": "active"}}}}

Solution

1. Step 1: Identify correct key for filtering

   The constant_score query uses the key "filter" to specify the filter clause, not "query" or direct term.

2. Step 2: Check filter syntax

   The filter should be a term query inside the filter object, correctly written as {"term": {"status": "active"}}.

3. Final Answer:

   {"constant_score": {"filter": {"term": {"status": "active"}}}} -> Option D

4. Quick Check:

   Use "filter" with term inside constant_score [OK]

Hint: Use "filter" key with term query inside constant_score [OK]

Common Mistakes:

• Using "query" instead of "filter"
• Placing term query directly under constant_score
• Using match instead of term for exact filter

3. Given this Elasticsearch query snippet, what will be the score of each matched document?

{
  "constant_score": {
    "filter": { "term": { "category": "books" } },
    "boost": 3
  }
}

medium

A. The score will vary based on relevance

B. The score will be 3 for all matched documents

C. The score will be 1 for all matched documents

D. The score will be 0 because boost is ignored

Solution

1. Step 1: Understand constant_score with boost

   The constant_score query assigns the same score to all matched documents, and the boost multiplies that score.

2. Step 2: Calculate the score

   By default, constant_score gives score 1, multiplied by boost 3, resulting in score 3 for all matches.

3. Final Answer:

   The score will be 3 for all matched documents -> Option B

4. Quick Check:

   constant_score x boost = 3 [OK]

Hint: Boost multiplies constant score, so score = boost value [OK]

Common Mistakes:

• Assuming scores vary by relevance
• Ignoring the boost value
• Thinking boost is ignored in constant_score

4. Identify the error in this constant score query:

{
  "constant_score": {
    "filter": {
      "terms": {
        "tags": ["tech", "science"]
      }
    },
    "boost": "2"
  }
}

medium

A. The boost value should be a number, not a string

B. The filter key should be replaced with query

C. The terms query cannot be used inside constant_score

D. The tags field should be inside a match query

Solution

1. Step 1: Check boost data type

   The boost parameter must be a numeric value, not a string. Here, "2" is a string, which is invalid.

2. Step 2: Validate filter and terms usage

   Using "filter" with a "terms" query is valid syntax, so no error there.

3. Final Answer:

   The boost value should be a number, not a string -> Option A

4. Quick Check:

   boost must be numeric, not string [OK]

Hint: Boost must be a number, not quoted string [OK]

Common Mistakes:

• Using string for boost instead of number
• Replacing filter with query incorrectly
• Misunderstanding terms query usage

5. You want to find all documents where status is published and boost their score by 5, but keep all matched documents scored equally. Which query correctly achieves this?

hard

A. { "match": { "status": "published", "boost": 5 } }

B. { "bool": { "must": { "term": { "status": "published" } }, "boost": 5 } }

C. { "constant_score": { "filter": { "term": { "status": "published" } }, "boost": 5 } }

D. { "constant_score": { "query": { "term": { "status": "published" } }, "boost": 5 } }

Solution

1. Step 1: Use constant_score with filter and boost

   To keep scores equal and apply a boost, use constant_score with a filter clause and boost parameter.

2. Step 2: Validate correct syntax

   { "constant_score": { "filter": { "term": { "status": "published" } }, "boost": 5 } } uses "filter" with a term query and numeric boost, which is the correct syntax.

3. Step 3: Check other options

   { "bool": { "must": { "term": { "status": "published" } }, "boost": 5 } } uses bool query which scores by relevance, not constant. { "match": { "status": "published", "boost": 5 } } is a match query with boost but scores vary. { "constant_score": { "query": { "term": { "status": "published" } }, "boost": 5 } } incorrectly uses "query" instead of "filter" inside constant_score.

4. Final Answer:

   { "constant_score": { "filter": { "term": { "status": "published" } }, "boost": 5 } } -> Option C

5. Quick Check:

   constant_score + filter + boost = equal boosted scores [OK]

Hint: Use constant_score with filter and numeric boost for equal boosted scores [OK]

Common Mistakes:

• Using query instead of filter inside constant_score
• Using bool or match queries that score variably
• Setting boost as string instead of number