There is no DBI method that will reliably give you a count of the number of rows fetched. Two things I can think of to do:

  1. if you intend to process all the rows of your
     original fetch anyway, then just count the rows as
     you process them - that is *the* most reliable way
     to get a count of rows fetched.

  2. use the 'count(*)' which will retrieve one column(that
     being the number of rows fetched), and in this example
     I assigned the count to alias 'count':
     
     $dbh->{RaiseError} = 1; # save having to check each method call

     my $sql = qq{
         SELECT count(*) as count
         FROM your_table
         WHERE one_of_the_columns = something
     };
     my $sth = $dbh->prepare($sql);
     $sth->execute;
     my ($count) = $sth->fetchrow_array;
     if ($count == 0) {
        print "NO rows fetched!\n";
     }
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HTH.