---
title: LowCardinality Data Type reference
meta:
    description: Dictionary-encoded representation of data types.
headingMaxLevels: 2
---

# LowCardinality(T)

This data type wraps another data type, optimizing its storage and query performance by using dictionary encoding for columns with low cardinality.

## Syntax

```sql
LowCardinality(data_type)
```

### Arguments

- `data_type`: Type. The underlying data type to be dictionary-encoded. This can be `String`, `FixedString`, `Date`, `DateTime`, or numeric types (excluding `Decimal`).

## Description

The `LowCardinality` data type modifies the internal storage and processing of data by applying dictionary encoding. This technique can significantly boost the performance of `SELECT` queries, especially for columns that contain a limited number of unique values.

The effectiveness of `LowCardinality` depends on the diversity of the data. It generally provides better efficiency for both data storage and retrieval when a column has fewer than 10,000 distinct values. However, if a column contains more than 100,000 distinct values, using `LowCardinality` might lead to worse performance compared to standard data types.

For string columns, `LowCardinality` is often a more flexible and equally or more efficient alternative to the `Enum` data type.

## Example

You typically define `LowCardinality` types when creating a Data Source schema.

```tb {% title="lc_s.datasource" %}
SCHEMA >
    `s` LowCardinality(String)

ENGINE "MergeTree"
```

You can also cast values to `LowCardinality` within a `SELECT` query:

```sql
SELECT toLowCardinality('Tinybird') AS lc_string;
```

Result:

```result
┌─lc_string─┐
│ Tinybird  │
└───────────┘
```

## Related functions

- [toLowCardinality](../functions/type-conversion-functions#tolowcardinality)
- [lowCardinalityKeys](../functions/other-functions#lowcardinalitykeys)
- [lowCardinalityIndices](../functions/other-functions#lowcardinalityindices)