Can’t Query Between Databases on Azure SQL Due to Private Endpoint Issues

One of the only solutions available is to add the SQL public IP of your region to your configuration. Alternatively, you might get around this by using 127.0.0.1 and a local user for the connection.

Just so you know, Elastic Database Query is still in preview mode. It doesn't function quite like cross-database queries in Azure SQL Managed Instances or on SQL Server. If your project requires high-performance queries across databases, it might be a good idea to switch to a Managed Instance instead.

This is definitely a known limitation in Azure SQL. The error message can be confusing. Even though your databases are on the same server, external queries need to follow specific network rules. When public access is turned off and a private endpoint is set up, the connection fails because it's trying to reach out through public channels unless you've set things up to allow otherwise. It’s frustrating and catches a lot of people off guard! There are a few ways to work around this depending on your architecture.

You also need to make sure that the target database allows network access from Azure services and resources. Generally, traffic between the two databases needs to route through a gateway since it can't go through a private endpoint.