my $dbh = DBI->connect($DNS, {RaiseError=>1});
my $sth = $dbh->prepare(qq{SELECT product, price, quantity 
FROM products 
WHERE quantity < ? });		

$sth->execute(100);
sub ask_customer {
	# display product details
	# ask customer input 
	# do something smart with customer answer
}

while (my ($product, $price, $quantity) = $sth->fetchrow_array()) {
	ask_customer ($product, $price, $quantity);
}
$dbh->disconnect();

##</code><code>##

+----------------------+   +-----------------------+
|       customer       |   |          order        |
+-----+--------+-------+   +--------+--------+-----+
| ID  | name   | state |   | custID | prodID | qty |
+-----+--------+-------+   +--------+--------+-----+
| C01 | Joe    | NY    |   | C02    | P03    |   9 |
| C02 | Frank  | NY    |   | C02    | P01    |   2 |
| C03 | Bill   | TX    |   | C02    | P02    | 200 |
| C04 | Moe    | MA    |   | C05    | P01    |   3 |
| C05 | Sue    | CA    |   | C05    | P02    | 450 |
+-----+--------+-------+   | C01    | P04    |   5 |
                           | C01    | P03    |   1 |
+----------------------+   +--------+--------+-----+
|       product        |
+-----+-------+--------+
| ID  | price | name   |
+-----+-------+--------+
| P01 | 1.90  | hammer |
| P02 | 0.05  | nail   |
| P03 | 5.50  | pliers |
| P04 | 4.00  | cutter |
+-----+-------+--------+

##</code><code>##

my @customers = (
    [ 'C01', 'Joe',   'NY' ],
	[ 'C02', 'Frank', 'NY' ],
	[ 'C03', 'Bill',  'TX' ],
	[ 'C04', 'Moe',   'MA' ],
	[ 'C05', 'Sue',   'CA' ]
);

my @products = (
   [ 'P01', 'hammer', 1.90 ],
   [ 'P02', 'nail',   0.05 ],
   [ 'P03', 'pliers', 5.50 ],
   [ 'P04', 'cutter', 4.00 ]
);

my @orders = (
   [ 'C02', 'P03',   9 ],
   [ 'C02', 'P01',   2 ],
   [ 'C02', 'P02', 200 ],
   [ 'C05', 'P01',   3 ],
   [ 'C05', 'P02', 450 ],
   [ 'C01', 'P04',   4 ],
   [ 'C01', 'P03',   1 ]
 );

##</code><code>##

SELECT cust.name AS customer, prod.name AS product,
price, qty, qty*price AS total
FROM order
    INNER JOIN customer cust ON (cust.ID = custID)
    INNER JOIN product prod ON (prod.ID = prodID)
+------------------------------------------+
|                query results             |
+----------+---------+-------+-----+-------+
| customer | product | price | qty | total |
+----------+---------+-------+-----+-------+
| Frank    | pliers  |  5.50 |   9 | 49.50 |
| Frank    | hammer  |  1.90 |   2 |  3.80 |
| Frank    | nail    |  0.05 | 200 | 10.00 |
| Sue      | hammer  |  1.90 |   3 |  5.70 |
| Sue      | nail    |  0.05 | 450 | 22.50 |
| Joe      | cutter  |  4.00 |   5 | 20.00 |
| Joe      | pliers  |  5.50 |   1 |  5.50 |
+----------+---------+-------+-----+-------+

SELECT cust.name AS customer, SUM(qty*price) AS total
FROM order
    INNER JOIN customer cust ON (cust.ID = custID)
    INNER JOIN product prod ON (prod.ID = prodID)
GROUP BY customer
+------------------+
|  query results   |
+----------+-------+
| customer | total |
+----------+-------+
| Frank    | 63.30 |
| Sue      | 28.20 |
| Joe      | 25.50 |
+----------+-------+

##</code><code>##

my %orders_by_customer = (
'Frank' => [ { product => 'pliers',  qty =>   9 },
             { product => 'hammer',  qty =>   2 },
             { product => 'nail',    qty => 200 }
           ] ,
'Sue'   => [ { product => 'hammer',  qty =>   3 },
             { product => 'nail',    qty => 450 }
           ] ,
'Joe'   => [ { product => 'cutter',  qty =>   5 },
             { product => 'pliers',  qty =>   1 }
           ] 
);

##</code><code>##

my %orders_by_customer = ();
while (my $href = $sth->fetchrow_hashref()) {
    my %order = (
        'product' => $href->{'product'}, 
        'qty' => $href->{qty}
   );
   push @{$orders_by_customer{$href->{'customer'}}}, \%order;
}

##</code><code>##

 
	my $surname = 'Jones';
	my $query= 
        qq{SELECT name, surname FROM employees WHERE surname = $surname };
	my $sth = $dbh->prepare($query);
	$sth->execute();

##</code><code>##

 
	my $query= qq{SELECT name, surname FROM employees WHERE surname = ? };
	my $sth = $dbh->prepare($query);
	$sth->execute('Jones');