my $row_checker = "select count(col1) from table1 where col1 = ? and col2 = ? and col3 = ?";
$row_checker = $dbh -> prepare($row_checker);

# or ...

my $updater = $dbh -> prepare(qq{ 
        update table1 set col1 = ?, col2 = ?, col3 = ?
                where col1 = ? and col2 = ? and col3 = ?
});