#! perl
use strict;
use warnings;
use feature qw( say );

my  $hour           = 12;
my  $error          = 'Submission_user_error';
my  $sub_user_error =  3;
my  $number         = 42;
my  %db_error_data;
    $db_error_data{$hour}{$error}{$sub_user_error} =  0;

say 'With ||:';
say $db_error_data{$hour}{$error}{$sub_user_error} || 0, $number;

say 'With or:';
say $db_error_data{$hour}{$error}{$sub_user_error} or 0, $number;