my $dbh = DBI->connect($conn_string, $user, $password,
{
    RaiseError => 1,
}) || die $DBI::errstr;

my $sth = $dbh->prepare(<<__END_SQL__);
SELECT stuff
  FROM some_place
 WHERE some_condition = 1
__END_SQL__

$sth->execute;

my $num_rows = 0;
while (my @x = $sth->fetchrow)
{
    $num_rows++;
    do_something_with(@x);
}

die "No rows found\n" unless $num_rows;

print "Done\n";