id    fname    lname
1     Joe      Smith
2     Sally    Smith

##</code><code>##

use DBI;
$dbh = DBI->connect("DBI:CSV:f_dir=./");
$query = "select id, fname, lname";
$sth->prepare($query);
$sth->execute();
while ($rowdata = $sth->fetchrow_hashref) {
    $hash{$rowdata->{'id'}} = $rowdata{'id'};
    if ($rowdata->{'fname'}) { $hash{$rowdata->{'id'}}{'fname'} = 1; }
    if ($rowdata->{'lname'}) { $hash{$rowdata->{'id'}}{'lname'} = 1; }
}

print Dumper(\%hash);

##</code><code>##

$VAR1 = {
          '' => undef
        };

##</code><code>##

$VAR1 = {
            {
              '' => 1
              'fname' => 'John'
              'lname' => 'Smith'
            {
            {
              '' => 2
              'fname' => 'Sally'
              'lname' => 'Smith'
            {
        };