$sth->execute();
my $recordset = $sth->fetchall_arrayref();
if (@$recordset) {
   # there are records. Do something here
}
else {
   # empty recordset. Do something else.
}

##</code><code>##

my $found = 0;
while (my $rec = $sth->fetchrow_arrayref()) {
   #do something
   $found = 1;
}
unless ($found) {
   # recordset was empty.
   # do something else
}