@Nick Chuah
Thank you for the question and for using Microsoft Q&A platform.
Azure Cosmos DB for PostgreSQL does not currently support the oracle_fdw extension. This extension is available for Azure Database for PostgreSQL - Flexible Server, which allows you to create foreign tables in PostgreSQL that connect to Oracle tables or schemas.
https://techcommunity.microsoft.com/blog/adforpostgresql/introducing-support-for-oracle-fdw-extension-in-azure-database-for-postgresql/4296504
The available extensions for Azure Cosmos DB are listed here:
https://learn.microsoft.com/en-us/azure/cosmos-db/postgresql/reference-extensions
If you need to use the oracle_fdw extension, you should consider using Azure Database for PostgreSQL - Flexible Server instead of Azure Cosmos DB for PostgreSQL.
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