Maybe something along these lines? (Untested):

my @fields = my ( $cat, $schem, $tn, $cn, $dt, $tyn, $cs, $bl, $dd, $n
+pr, $nul) = $sth->fetchrow_array()
my $num_fields = @fields; #0-indexed number of fields, ie 10 if there 
+are 11 fields.

$field_index = 0;
while ( $cat, $schem, $tn, $cn, $dt, $tyn, $cs, $bl, $dd, $npr, $nul )
+ { 
      print "\t$cn ";
      if (($tyn eq 'DATETIME') || ($tyn eq 'DOUBLE')) {
         print "$tyn";
      } else {
         print "$tyn($cs)";
      }
      print " not null" if ($nul == 0);
      # need to put a condition on adding the comma to not add the com
+ma on the last loop.
      if ( $field_index < $num_fields) {
          print ",\n";  
      }
      $field_index++;
   }
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Actually, the other solutions are a lot nicer, but... you know... timtowtdi... :)