I don't believe you will be able to get COLUMNAR data. All you will get is something like UNABLE TO INSERT NULL... unless you use custom error messages.
However, an easy way of troubleshooting is to build your SQL string as a STRING and write that to a TEMPORARY REAL table for review. I have done this many times and when you review the data (v. variables) most of the time it sticks out like a sore thumb. Also, this way allows you to run the statement(s) in QA to see what happens