> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-mintlify-3a82795f.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

> The DataLakeCatalog database engine enables you to connect ClickHouse to external data catalogs and query open table format data

# DataLakeCatalog

The `DataLakeCatalog` database engine enables you to connect ClickHouse to external
data catalogs and query open table format data without the need for data duplication.
This transforms ClickHouse into a powerful query engine that works seamlessly with
your existing data lake infrastructure.

<h2 id="supported-catalogs">
  Supported catalogs
</h2>

The `DataLakeCatalog` engine supports the following data catalogs:

* **AWS Glue Catalog** - For Iceberg tables in AWS environments
* **Databricks Unity Catalog** - For Delta Lake and Iceberg tables
* **Hive Metastore** - Traditional Hadoop ecosystem catalog
* **REST Catalogs** - Any catalog supporting the Iceberg REST specification

<h2 id="creating-a-database">
  Creating a database
</h2>

You will need to enable the relevant settings below to use the `DataLakeCatalog` engine:

```sql theme={null}
SET allow_experimental_database_iceberg = 1;
SET allow_experimental_database_unity_catalog = 1;
SET allow_experimental_database_glue_catalog = 1;
SET allow_experimental_database_hms_catalog = 1;
SET allow_experimental_database_paimon_rest_catalog = 1;
```

Databases with the `DataLakeCatalog` engine can be created using the following syntax:

```sql theme={null}
CREATE DATABASE database_name
ENGINE = DataLakeCatalog(catalog_endpoint[, user, password])
SETTINGS
catalog_type,
[...]
```

The following settings are supported:

| Setting                 | Description                                                                                                 |
| ----------------------- | ----------------------------------------------------------------------------------------------------------- |
| `catalog_type`          | Type of catalog: `glue`, `unity` (Delta), `rest` (Iceberg), `hive`, `onelake` (Iceberg)                     |
| `warehouse`             | The warehouse/database name to use in the catalog.                                                          |
| `catalog_credential`    | Authentication credential for the catalog (e.g., API key or token)                                          |
| `auth_header`           | Custom HTTP header for authentication with the catalog service                                              |
| `auth_scope`            | OAuth2 scope for authentication (if using OAuth)                                                            |
| `storage_endpoint`      | Endpoint URL for the underlying storage                                                                     |
| `oauth_server_uri`      | URI of the OAuth2 authorization server for authentication                                                   |
| `vended_credentials`    | Boolean indicating whether to use vended credentials from the catalog (supports AWS S3 and Azure ADLS Gen2) |
| `aws_access_key_id`     | AWS access key ID for S3/Glue access (if not using vended credentials)                                      |
| `aws_secret_access_key` | AWS secret access key for S3/Glue access (if not using vended credentials)                                  |
| `region`                | AWS region for the service (e.g., `us-east-1`)                                                              |
| `dlf_access_key_id`     | Access key ID for DLF access                                                                                |
| `dlf_access_key_secret` | Access key Secret for DLF access                                                                            |

<h2 id="examples">
  Examples
</h2>

See below sections for examples of using the `DataLakeCatalog` engine:

* [Unity Catalog](/guides/use-cases/data-warehousing/unity-catalog)
* [Glue Catalog](/guides/use-cases/data-warehousing/glue-catalog)
* OneLake Catalog
  Can be used by enabling `allow_experimental_database_iceberg` or `allow_database_iceberg`.

```sql theme={null}
CREATE DATABASE database_name
ENGINE = DataLakeCatalog(catalog_endpoint)
SETTINGS
   catalog_type = 'onelake',
   warehouse = warehouse,
   onelake_tenant_id = tenant_id,
   oauth_server_uri = server_uri,
   auth_scope = auth_scope, 
   onelake_client_id = client_id, 
   onelake_client_secret = client_secret;
SHOW TABLES IN database_name;
SELECT count() from database_name.table_name;
```