my $update = {
        ADDRESS       => 'test',
        customer_name => 'eric' };

my @cols = sort grep { defined $update->{$_}} keys %$update;
my $sql = join (",", map { "$_ = ?" } @cols );
print "UPDATE test SET $sql WHERE id = ?";
#then you can use it like:
# $dbh->execute("UPDATE test SET $sql WHERE id = ?",undef, map {%update{$_}} @cols, $id);