my $sql2 = qq/
  INSERT INTO transaction_details (quantity, gross_sales)
              VALUES (?, ?)
/;

my $sth = $dbh->prepare($sql2);

while (<>) {  
    my $quantity = param("quantity");
    my $gross_sales = param("gross_sales");
     
    my $rv = $sth->execute($quantity, $gross_sales);
    # Handle error if $rv is false...
}