Ah yes, quite right. I missed that in my haste.

OP, the function you're calling doesn't appear to be standard DBI, so I can't advise you (the OP) on how to handle exceptions, but in general, it will probably be one of the following:

• The function might die() on error; use eval
• It may return an empty list, in which case your $mx_registered_process_id will be undef (but undef might also indicate something else, such as a NULL column, so be careful; assign the function return to an intermediary @array if that's the case).
• It may use a package scalar to hold error values (which is set to undef if there was no error.

Again, this is all just speculative, since I don't know the semantics of your db_select_row() function.