It looks like a flip-flop ... (update: in Perl you can also use a variable as it's own flag provided there are no empty or zero values for it permitted in the actual data)

# ...

$sth->bind_columns( undef,\$alias);
my $key = 0;
while($sth->fetchrow_array()) {

    if ( $key  ) {
        print "$key, $alias\n";
        $key = 0;
    }
    else{
        $key = $alias;
    }
}
[download]

or if you later realise you need to store the pairs anyway... ;)

$sth->bind_columns( undef,\$alias);
my %hash;
my $key = 0;
while($sth->fetchrow_array()) {

    if ( $key  ) {
        $hash{ $key } = $alias;
        # print "$key, $alias\n";
        $key = 0;
    }
    else{
        $key = $alias;
    }
}
[download]

(updated to get rid of an unnecessary step)