# Usage: my $iter = DbiSthIterator->new($sth1, $sth2, ...);
#
#        while ($row = $iter->next()) {
#            ...undef signals the exhaustion of the iterator
#        }

package DbiSthIterator;

sub new {
    my ($class, @sth) = @_;
    bless \@sth, $class;
}

sub next {
    my $self = shift;

    while (my $sth = shift(@$self)) {
        if (my $row = $sth->fetchrow_hashref()) {
            push(@$self, $sth);
            return $row;
        } else {
            # Leaving the exhausted $sth out of the queue
            next;
        }
    }

    undef;
}

1;