Thank you hippo for pointing this out, however, the snippet I've inserted into my recent post, is the piece of code, that was removed and replaced by the code, that roboticus kindly suggested to me in his post.

So instead of:

my $SQL = "INSERT INTO $table VALUES (" 
        . join(",", map { "?" } $csv->fields)
        . ")";
$prep = $db->prepare($SQL) or die "...";
while (my $row = $csv->getline($fh)) {
    $prep->execute($csv->fields);
}
[download]

I used:

my $SQL = "INSERT INTO $table VALUES (" 
        . join(",", map { "?" } $csv->fields)
        . ")";
$prep = $db->prepare($SQL) or die "Cannot prepare database";
while (my $row = $csv->getline($fh)) {
    $prep->execute($csv->fields);
}
[download]

It does not change the fact, that I still struggle with this new error: