This technique is extremly usesful if your ZSQL methods are throwing exceptions like 'ambiguous column' and giving you no clue as to where the error is. Simply create a DTMLMethod like the one below, grab the generated SQL and paste it into another tool that will give you more informative feedback (eg. SQL*Plus)::

The magic here is the 'src__=1' argument which tells the ZSQL method that we want to view the SQL rather than execute it and return the results.