---
title: BM25 Scoring
description: BM25 scores sort the result set by relevance
canonical: https://docs.paradedb.com/documentation/sorting/score
---

BM25 scores measure how relevant a score is for a given query. Higher scores indicate higher relevance.

## Basic Usage

The `pdb.score(<key_field>)` function produces a BM25 score and can be added to any query where any of the ParadeDB operators are present.

<CodeGroup>
```sql SQL
SELECT id, pdb.score(id)
FROM mock_items
WHERE description ||| 'shoes'
ORDER BY pdb.score(id) DESC
LIMIT 5;
```

```ts Drizzle
import { desc } from "drizzle-orm";
import { search } from "@paradedb/drizzle-paradedb";

await db
  .select({
    id: mockItems.id,
    score: search.score(mockItems.id),
  })
  .from(mockItems)
  .where(search.matchAny(mockItems.description, "shoes"))
  .orderBy(desc(search.score(mockItems.id)))
  .limit(5);
```

```python Django
from paradedb import MatchAny, ParadeDB, Score

MockItem.objects.filter(
    description=ParadeDB(MatchAny('shoes'))
).annotate(
    score=Score()
).values('id', 'score').order_by('-score')[:5]
```

```python SQLAlchemy
from sqlalchemy import desc, select
from sqlalchemy.orm import Session
from paradedb.sqlalchemy import pdb, search

stmt = (
    select(MockItem.id, pdb.score(MockItem.id).label("score"))
    .where(search.match_any(MockItem.description, "shoes"))
    .order_by(desc("score"))
    .limit(5)
)

with Session(engine) as session:
    session.execute(stmt).all()
```

```ruby Rails
MockItem.search(:description)
        .matching_any("shoes")
        .with_score
        .select(:id)
        .order(search_score: :desc)
        .limit(5)
```

```cs EF Core
await dbContext
    .MockItems.Where(item => EF.Functions.MatchAny(item.Description, "shoes"))
    .Select(item => new { item.Id, Score = EF.Functions.Score(item.Id) })
    .OrderByDescending(item => item.Score)
    .Take(5)
    .ToListAsync();
```

</CodeGroup>

In order for a field to be factored into the BM25 score, it must be present in the BM25 index. For instance,
consider this query:

<CodeGroup>
```sql SQL
SELECT id, pdb.score(id)
FROM mock_items
WHERE description ||| 'keyboard' OR rating < 2
ORDER BY pdb.score(id) DESC
LIMIT 5;
```

```ts Drizzle
import { desc, lt, or } from "drizzle-orm";
import { search } from "@paradedb/drizzle-paradedb";

await db
  .select({
    id: mockItems.id,
    score: search.score(mockItems.id),
  })
  .from(mockItems)
  .where(
    or(
      search.matchAny(mockItems.description, "keyboard"),
      lt(mockItems.rating, 2),
    ),
  )
  .orderBy(desc(search.score(mockItems.id)))
  .limit(5);
```

```python Django
from django.db.models import Q
from paradedb import MatchAny, ParadeDB, Score

MockItem.objects.filter(
    Q(description=ParadeDB(MatchAny('keyboard'))) | Q(rating__lt=2)
).annotate(
    score=Score()
).values('id', 'score').order_by('-score')[:5]
```

```python SQLAlchemy
from sqlalchemy import desc, or_, select
from sqlalchemy.orm import Session
from paradedb.sqlalchemy import pdb, search

stmt = (
    select(MockItem.id, pdb.score(MockItem.id).label("score"))
    .where(or_(search.match_any(MockItem.description, "keyboard"), MockItem.rating < 2))
    .order_by(desc("score"))
    .limit(5)
)

with Session(engine) as session:
    session.execute(stmt).all()
```

```ruby Rails
MockItem.search(:description)
        .matching_any("keyboard")
        .or(MockItem.where(rating: ...2))
        .with_score
        .select(:id)
        .order(search_score: :desc)
        .limit(5)
```

```cs EF Core
await dbContext
    .MockItems.Where(item =>
        EF.Functions.MatchAny(item.Description, "keyboard") || item.Rating < 2
    )
    .Select(item => new { item.Id, Score = EF.Functions.Score(item.Id) })
    .OrderByDescending(item => item.Score)
    .Take(5)
    .ToListAsync();
```

</CodeGroup>

While BM25 scores will be returned as long as `description` is indexed, including `rating` in the BM25 index definition will allow results matching
`rating < 2` to rank higher than those that do not match.

## Joined Scores

First, let's create a second table called `orders` that can be joined with `mock_items`:

```sql
CALL paradedb.create_bm25_test_table(
  schema_name => 'public',
  table_name => 'orders',
  table_type => 'Orders'
);

ALTER TABLE orders
ADD CONSTRAINT foreign_key_product_id
FOREIGN KEY (product_id)
REFERENCES mock_items(id);

CREATE INDEX orders_idx ON orders
USING bm25 (order_id, product_id, order_quantity, order_total, customer_name)
WITH (key_field = 'order_id');
```

Next, let's compute a "combined BM25 score" over a join across both tables.

<Note>
  Directly computing and ordering by the sum of scores across a join (e.g.
  `ORDER BY pdb.score(t1) + pdb.score(t2)`) is currently not efficient. For more
  details on implementing efficient support for this operation, please refer to
  [Issue #5300](https://github.com/paradedb/paradedb/issues/5300).
</Note>

The recommended approach for combining scores from multiple tables is to use [Reciprocal Rank Fusion (RRF)](https://www.paradedb.com/learn/search-concepts/reciprocal-rank-fusion). RRF combines the ranked results from separate queries into a single unified ranking.

<CodeGroup>
```sql SQL
WITH order_search AS (
  SELECT order_id, RANK() OVER (ORDER BY score DESC) AS rank
  FROM (
    SELECT order_id, pdb.score(order_id) AS score
    FROM orders
    WHERE customer_name ||| 'Johnson'
    ORDER BY pdb.score(order_id) DESC
    LIMIT 20
  )
),
product_search AS (
  SELECT o.order_id, RANK() OVER (ORDER BY score DESC) AS rank
  FROM (
    SELECT id, pdb.score(id) AS score
    FROM mock_items
    WHERE description ||| 'running shoes'
    ORDER BY pdb.score(id) DESC
    LIMIT 20
  ) m
  JOIN orders o ON o.product_id = m.id
),
rrf AS (
  SELECT order_id, 1.0 / (60 + rank) AS s FROM order_search
  UNION ALL
  SELECT order_id, 1.0 / (60 + rank) AS s FROM product_search
)
SELECT
  o.order_id,
  o.customer_name,
  m.description,
  sum(rrf.s) AS score
FROM rrf
JOIN orders o USING (order_id)
JOIN mock_items m ON o.product_id = m.id
GROUP BY o.order_id, o.customer_name, m.description
ORDER BY score DESC, o.order_id
LIMIT 5;
```

</CodeGroup>

## Score Refresh

The scores generated by the BM25 index may be influenced by dead rows that have not been cleaned up by the `VACUUM` process.

Running `VACUUM` on the underlying table will remove all dead rows from the index and ensures that only rows visible to the current
transaction are factored into the BM25 score.

```sql
VACUUM mock_items;
```

This can be automated with [autovacuum](/documentation/performance-tuning/overview).
