How can I check if a database query will return results?

sub list {
  require HTTP::Date;
  import HTTP::Date;

  my $date = [split /s+/, HTTP::Date::time2iso(time())]->[0];

  my $dbh = DBI->connect($dsn, $user, $password)
    || die "cannot connect to $database: $!n";

  my $sql = <<EOSQL;
SELECT * FROM $table where expiry >= '$date' order by expiry
EOSQL

  my $sth = $dbh->prepare($sql);
  $sth->execute();


  while (my $ref = $sth->fetchrow_hashref()) {
    my $temp  = $template;
    $temp     =~ s#__TITLE__#$ref->{'title'}#;

    my $job_spec = $ref->{'job_spec'};

...etc...

$sth->execute();

my $first = 1;
while (my $ref = $sth->fetchrow_hashref()) {
    if( $first ) {
        print "We currently have the following vacancies:n";
        $first = 0;
    }
    my $temp  = $template;
    ...
}
if( $first ) {
    print "No vacancies foundn";
}

$sth->execute();

if($sth->rows) {
  print "We have data!n";
}

while(my $ref = $sth->fetchrow_hashref()) {
...
}

$sth->execute();

my $ref = $sth->fetchrow_hashref();
if ($ref) {
  print "We currently have the following vacancies:n";
  while ($ref) {
    my $temp  = $template;
    ...
    $ref = $sth->fetchrow_hashref();
  }
} else {
    print "No vacancies foundn";
}

my @results = ();
while (my $ref = $sth->fetchrow_hashref()) {
   push @results, $ref;
}

if ($#results == 0) {
  ... no results
} else {
  foreach $ref (@results) {
    my $temp = $template;
    ....
 }

my $output = '';

$output .= "whatever we would have printed";

if ($output eq '')
{
  print 'We have no vacancies.';
}
else
{
  print "We currently have the following vacancies:n" . $output;
}

use Lingua::EN::Inflect 'PL';

$sth->execute();
my $results = $sth->fetchall_arrayref( {}, $max_rows );

if (@$results) {
    print "We currently have the following ", PL("vacancy",scalar @$results), ":n";

    for my $ref (@$results) {
        ...
    }
}

# count the vacancies
$numinfo = $dbh->prepare("SELECT COUNT(*) FROM $table WHERE EXPIRY >= ?");
$numinfo->execute($date);
$count = $numinfo->fetchrow_arrayref()->[0];

# print a message
my $msg = '';
if   ($count == 0) $msg = 'We do not have any vacancies right now';
else               $msg = 'We have the following vacancies';
print($msg);

For a non-"SELECT" statement, "execute" returns the number of rows
 affected, if known. If no rows were affected, then "execute"
 returns "0E0", which Perl will treat as 0 but will regard as true.

my $returnval = $sth->execute;
 if (defined $returnval && $returnval == 0) {
     carp "Query executed successfully but returned nothing";
     return;
 }