I'm glad you asked that, because it forced me to take a hard look at the full create statement (as given by show create table reference_code (Did I mention I'm using a mysql db?)):

CREATE TABLE `reference_code` (
  `processor` enum('PTP','GNC') default NULL,
  `code` varchar(255) NOT NULL default '',
  `explanation` text NOT NULL
)
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(minus indexes and other miscellanea) It's interesting that the two columns that have defaults specified don't need their respective variables ( $1 and $2) messed with. I tried recreating the table with a default for the explanation column, but apparently blob's can't have defaults as the default option was silently dropped. I also checked to see if, after a successful run of the script (using the  my $x=$3; method), any "processor" values were null or any "code" values were '', and they weren't.