I had to do some review of this because it can get confusing.

By design you can't get number of rows out of a SELECT statement. You can only get a numerical result out of DELETE or UPDATE statements. The question is how to get that info from Perl DBI? There are 2 ways:

First with a do statement:
 my $rows = $dbh->do("DELETE FROM table_name WHERE col2='X'");
$rows can be a) Integer>0 b) 0E0 c) undef
0E0 is the DB's "true but numeric zero result".
undef would mean the statement failed.

Second with prepare/execute:

my $sth= $dbh->prepare("DELETE FROM table_name WHERE col2=?");
$sth->execute("X");
my $rows = $sth->rows();
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$rows can be (like first example): a) Integer>0 b) 0E0 c) undef

I almost always run with RaiseError=1 so checking for undef doesn't come up.

I don't know if DBI returns 1 or 0E0 for a successful SELECT operation.