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while(@row = $sth->fetchrow_array) {
   ++$duplicate;
}

my $dbh = DBI->connect($dsn, $usr, $pwd, {RaiseError => 1});
my $sth = $dbh->prepare("insert into Customers(Names, ...) values(?, .
+..)");
...
    # Handle this the same way that you would handle the
    # case where your checkDuplicateName() returns true
 }