$mysql = $dbh->exec ( $sql );
for (my $i = 0; $i < @{$mysql}; $i++) {
    my $field1 = $mysql->[$i]{‘field1’};
    my $field2 = $mysql->[$i]{‘field2’};

or…

$mysql = $dbh->exec ( $sql );
foreach (@$mysql) {
    my $field1 =  $_->{ ‘field1’ };
    my $field2 =  $_->{ ‘field2’ };