Constant score query in Elasticsearch - Step-by-Step Execution

Concept Flow - Constant score query

Start Query

↓

Apply Filter

↓

Wrap Filter in Constant Score

↓

Assign Fixed Score

↓

Return Results with Constant Score

↓

End

The constant score query wraps a filter and assigns a fixed score to all matching documents, ignoring relevance scoring.

Execution Sample

Elasticsearch

{
  "constant_score": {
    "filter": { "term": { "status": "active" } },
    "boost": 1.5
  }
}

This query finds documents where status is 'active' and assigns them a fixed score of 1.5.

Execution Table

Step	Action	Filter Applied	Score Assigned	Result
1	Start query execution	None	None	Query begins
2	Apply filter	status = 'active'	None	Documents filtered by status
3	Wrap filter in constant_score	status = 'active'	Fixed score 1.5	Score set to 1.5 for all matches
4	Return results	status = 'active'	1.5	Documents returned with constant score
5	End	N/A	N/A	Query execution complete

💡 All documents matching the filter receive the fixed score; no relevance scoring applied.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
Filtered Documents	None	Docs with status='active'	Docs with status='active'	Docs with status='active'
Score	None	None	1.5 (constant)	1.5 (constant)

Key Moments - 2 Insights

Why does the constant score query ignore relevance scoring?

Because the filter is wrapped in a constant_score query which assigns a fixed score (see execution_table step 3), so relevance scores from matching terms are not calculated.

What happens if the filter matches no documents?

No documents are returned because the filter excludes all (see execution_table step 2), so no scores are assigned or results returned.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what score is assigned to matching documents?

A Score of 0

B 1.5 fixed score

C Relevance score based on term frequency

D No score assigned

💡 Hint

Check the 'Score Assigned' column at step 3 in the execution_table.

At which step are documents filtered by the condition 'status = active'?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Filter Applied' column in the execution_table.

If the boost value changes from 1.5 to 2.0, what changes in the execution?

A The fixed score assigned changes to 2.0

B The filter changes to status='2.0'

C The documents filtered change

D No change in score

💡 Hint

The 'Score Assigned' column in execution_table step 3 shows the fixed score from boost.

Concept Snapshot

Constant score query syntax:
{
  "constant_score": {
    "filter": { ... },
    "boost": fixed_score
  }
}

Behavior:
- Filters documents by condition
- Assigns fixed score to all matches
- Ignores relevance scoring

Use when you want uniform scoring for filtered results.

Full Transcript

The constant score query in Elasticsearch wraps a filter and assigns a fixed score to all documents matching that filter. First, the query applies the filter condition to select documents. Then, it wraps this filter in a constant_score query which sets the score for all matched documents to a fixed value, ignoring the usual relevance scoring. This is useful when you want to treat all filtered documents equally in scoring. For example, filtering documents where status is 'active' and assigning them a score of 1.5 means all active documents have the same score regardless of term frequency or other factors. The execution steps show filtering first, then assigning the constant score, and finally returning the results. If no documents match the filter, no results are returned. Changing the boost value changes the fixed score assigned. This approach simplifies scoring when relevance is not important.