>type htmanning2.pl
use strict;
use warnings;

my @hash_rows = (
    {total => 3, other_col => 'fie'},
    {total => 6, other_col => 'fum'},
    {total => 5, other_col => 'oop'},
);

my %revenues = (
     3 => 30,
     6 => 48,
    10 => 50,
);

my $total_revenue;
foreach my $pointer (@hash_rows) {  # simulate fetchrow_hashref for post
    my $total = $pointer->{total};
    next if (!defined $total or !exists $revenues{$total});
    my $revenue = $revenues{$total};
    $total_revenue += $revenue;
    print "revenue: $revenue\ntotal_revenue $total_revenue\n\n";
}

>perl htmanning2.pl
revenue: 30
total_revenue 30

revenue: 48
total_revenue 78


>