@E H​ I thought I replied, but apparently I didn't -- apologies for the late response. So there are two different things in play:

• JDBC tables are supported by Apache Spark and as you can see in your screenshot, they work just fine in the Data Science & Engineering Workspace. However, they do NOT work in Databricks SQL. However, we are interested in supporting data sources like these but we're likely to support Redshift, MySQL etc. before we get to generic JDBC support. So, to be clear, the JDBC data source never worked in DBSQL.
• External Data Sources are different. They are part of the open source Redash product, but we are not planning on developing this feature right now.

What actual engine are you connecting to with the JDBC data source? Is it MySQL, Postgres etc?