Unless this is somehow 'magically' accomplished thru custom 2E pre-compiler process...
As far as I know, the only way to do SQL JOIN in 2E right now is thru SQL View (ex: virtual fields in file-to-file relationship). It is a very basic INNER JOIN, implemented with multiple files in the FROM and the join definition as part of the WHERE clause (ie: no INNER JOIN clause). And other JOIN types (ex: LEFT/RIGHT OUTER/EXCEPTION JOIN, etc) currently are not supported yet.