---
title: Top K
description: ParadeDB is optimized for quickly finding the Top K results in a table
canonical: https://docs.paradedb.com/documentation/sorting/topk
---

ParadeDB is highly optimized for quickly returning the Top K results out of the index. In SQL, this means queries that contain an `ORDER BY...LIMIT`:

<CodeGroup>
```sql SQL
SELECT description, rating, category
FROM mock_items
WHERE description ||| 'running shoes'
ORDER BY rating
LIMIT 5;
```

```python Django
from paradedb import Match, ParadeDB

MockItem.objects.filter(
    description=ParadeDB(Match('running shoes', operator='OR'))
).order_by('rating').values('description', 'rating', 'category')[:5]
```

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

stmt = (
    select(MockItem.description, MockItem.rating, MockItem.category)
    .where(search.match_any(MockItem.description, "running shoes"))
    .order_by(MockItem.rating)
    .limit(5)
)

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

```ruby Rails
MockItem.search(:description)
        .matching_any("running shoes")
        .order(:rating)
        .select(:description, :rating, :category)
        .limit(5)
```

</CodeGroup>

In order for a Top K query to be executed by ParadeDB vs. vanilla Postgres, all of the following conditions must be met:

1. All `ORDER BY` fields must be indexed. If they are text fields, they [must use the literal tokenizer](#sorting-by-text).
2. At least one ParadeDB text search operator must be present at the same level as the `ORDER BY...LIMIT`.
3. The query must have a `LIMIT`.
4. With the exception of `lower`, ordering by expressions is not supported -- only the raw fields themselves.

To verify that ParadeDB is executing the Top K, look for a `Custom Scan` with a `TopKScanExecState` in the `EXPLAIN` output:

```sql
EXPLAIN SELECT description, rating, category
FROM mock_items
WHERE description ||| 'running shoes'
ORDER BY rating
LIMIT 5;
```

<Accordion title = "Expected Response">
```csv
                                                                                                   QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=10.00..10.02 rows=3 width=552)
   ->  Custom Scan (ParadeDB Base Scan) on mock_items  (cost=10.00..10.02 rows=3 width=552)
         Table: mock_items
         Index: search_idx
         Segment Count: 1
         Exec Method: TopKScanExecState
         Scores: false
            TopK Order By: rating asc
            TopK Limit: 5
         Tantivy Query: {"with_index":{"query":{"match":{"field":"description","value":"running shoes","tokenizer":null,"distance":null,"transposition_cost_one":null,"prefix":null,"conjunction_mode":false}}}}
(10 rows)
```
</Accordion>

If any of the above conditions are not met, the query cannot be fully optimized and you will not see a `TopKScanExecState` in the `EXPLAIN` output.

## Tiebreaker Sorting

To guarantee stable sorting in the event of a tie, additional columns can be provided to `ORDER BY`:

<CodeGroup>
```sql SQL
SELECT description, rating, category
FROM mock_items
WHERE description ||| 'running shoes'
ORDER BY rating, id
LIMIT 5;
```

```python Django
from paradedb import Match, ParadeDB

MockItem.objects.filter(
    description=ParadeDB(Match('running shoes', operator='OR'))
).order_by('rating', 'id').values('description', 'rating', 'category')[:5]
```

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

stmt = (
    select(MockItem.description, MockItem.rating, MockItem.category)
    .where(search.match_any(MockItem.description, "running shoes"))
    .order_by(MockItem.rating, MockItem.id)
    .limit(5)
)

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

```ruby Rails
MockItem.search(:description)
        .matching_any("running shoes")
        .order(:rating, :id)
        .select(:description, :rating, :category)
        .limit(5)
```

</CodeGroup>

<Note>
  ParadeDB is currently able to handle 3 `ORDER BY` columns. If there are more
  than 3 columns, the `ORDER BY` will not be efficiently executed by ParadeDB.
</Note>

## Sorting by Text

If a text field is present in the `ORDER BY` clause, it must be indexed with the [literal](/documentation/tokenizers/available-tokenizers/literal) or
[literal normalized](/documentation/tokenizers/available-tokenizers/literal-normalized) tokenizer.

Sorting by lowercase text using `lower(<text_field>)` is also supported. To enable this, the expression `lower(<text_field>)` must be indexed
with either the literal or literal normalized tokenizer. See [indexing expressions](/documentation/indexing/indexing-expressions) for more information.

```sql
CREATE INDEX search_idx ON mock_items
USING bm25 (id, (lower(description)::pdb.literal))
WITH (key_field='id');
```

This allows sorting by lowercase to be optimized.

<CodeGroup>
```sql SQL
SELECT description, rating, category
FROM mock_items
WHERE description ||| 'sleek running shoes'
ORDER BY lower(description)
LIMIT 5;
```

```python Django
from django.db.models.functions import Lower
from paradedb import Match, ParadeDB

MockItem.objects.filter(
    description=ParadeDB(Match('sleek running shoes', operator='OR'))
).order_by(Lower('description')).values('description', 'rating', 'category')[:5]
```

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

stmt = (
    select(MockItem.description, MockItem.rating, MockItem.category)
    .where(search.match_any(MockItem.description, "sleek running shoes"))
    .order_by(func.lower(MockItem.description))
    .limit(5)
)

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

```ruby Rails
description = MockItem.arel_table[:description]
lower_description = Arel::Nodes::NamedFunction.new("LOWER", [description])

MockItem.search(:description)
        .matching_any("sleek running shoes")
        .order(Arel::Nodes::Ascending.new(lower_description))
        .select(:description, :rating, :category)
        .limit(5)
```

</CodeGroup>

## Sorting by JSON

Ordering by JSON subfield is on the roadmap but not yet supported. For example, this query will not receive an optimized
Top K scan:

```sql
SELECT id, description, metadata
FROM mock_items
WHERE description ||| 'sleek running shoes'
ORDER BY metadata->'weight'
LIMIT 5;
```
