Is your feature request related to a problem or challenge?

We only support to convert JOIN with ON constraint to SQL String now. The SQL as below can't be converted now.

SELECT * FROM orders JOIN customer USING (custkey)

It will panic with the message:

NotImplemented("Unsupported join constraint: Using")

Describe the solution you'd like

The unparse rule for JOIN in datafusion/sql/src/unparser/plan.rs should be implemented.

Describe alternatives you've considered

No response

Additional context

No response