Query an external PostgreSQL database directly from Databricks using Unity Catalog Lakehouse Federation

Steps

1. Create a Unity Catalog connection with CREATE CONNECTION <name> TYPE POSTGRESQL OPTIONS (host, port, user, and a reference to a Databricks secret rather than a literal password), requiring the CREATE CONNECTION privilege on the metastore.
2. Create a foreign catalog mirroring the external database with CREATE FOREIGN CATALOG <catalog> USING CONNECTION <name> OPTIONS (database '<db>'), requiring CREATE CATALOG privilege plus ownership or CREATE FOREIGN CATALOG privilege on the connection.
3. Browse the foreign catalog's schemas/tables in Catalog Explorer or via SQL just like a native Unity Catalog catalog.
4. Run federated queries, including cross-catalog joins with native Unity Catalog tables, and inspect the query plan to confirm predicate/column pushdown is occurring.
5. Apply Unity Catalog grants on the foreign catalog/schema/table to control access, since Lakehouse Federation enforces governance at the Databricks layer in addition to the source system's own permissions.