Federation Query

Federation Query lets you query data in external data systems (Hive, Databricks, Iceberg, Snowflake, etc.) directly using standard SQL — no data migration or copying required. By creating an EXTERNAL CATALOG, you map an external data catalog into Lakehouse for unified cross-system queries.

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Supported External Data Sources

External System	Connection Method	Typical Use Case
Apache Hive	Hive Metastore URIs	In-place acceleration of existing Hive warehouses, replacing Presto/Trino
Databricks Unity Catalog	Databricks API	Cross-platform federated analytics without moving Databricks data
Iceberg REST Catalog	Iceberg REST API	Query any data lake compatible with the Iceberg REST protocol
Snowflake Open Catalog	Iceberg REST API + OAuth	Access Iceberg tables managed by Snowflake

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Core Concepts

External Catalog is the entry point for federation queries. It maps the metadata catalog of an external data system into Lakehouse, accessed using three-level naming: catalog.schema.table.

External Schema is an alternative approach that mounts an external Hive database into the current workspace, using two-level naming schema.table. It is better suited for integrating a Hive database into an existing workspace.

Selection guide: External Catalog vs External Schema

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Quick Start

External Catalog depends on a pre-created Catalog Connection (Storage Connection → Catalog Connection → External Catalog). For the complete configuration steps, see the External Object User Guide.

Once configured, use standard SQL to query:

-- 1. Create an External Catalog (requires a Catalog Connection first) CREATE EXTERNAL CATALOG hive_prod CONNECTION hive_catalog_conn; -- 2. View all Catalogs (including external ones) SHOW CATALOGS; -- category = 'EXTERNAL' indicates a federated catalog -- 3. View Schemas and tables in the external Catalog SHOW SCHEMAS IN hive_prod; SHOW TABLES IN hive_prod.default; -- 4. Query directly without migrating data SELECT * FROM hive_prod.default.orders LIMIT 100; -- 5. Cross-system JOIN SELECT o.order_id, u.name FROM hive_prod.default.orders o JOIN my_lakehouse_table u ON o.user_id = u.id;

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This Section

Page	Description
External Object User Guide	Complete operations for creating, querying, and managing External Catalog / Schema / Table
Query Snowflake OpenCatalog Iceberg Tables	Federated queries on Snowflake-managed Iceberg data via Iceberg REST API
Databricks Cross-Platform Data Federation	Best practices for cross-platform federation between Databricks Unity Catalog and Singdata Lakehouse

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Related Documentation

• External Catalog Overview — Feature introduction, supported data sources, permission details
• External Catalog Federation Query Guide — Detailed operation examples and architecture principles
• Create External Catalog — DDL syntax reference
• Create Hive Catalog — Hive connection configuration details
• In-Place Lake Acceleration Guide — Complete guide for replacing Spark/Hive and Presto/Trino without moving data