You could avoid loading the entire table into memory by doing two reads («SELECT MAX(size)» and «SELECT qty, size, price ORDER BY qty ASC, size ASC»).

my $max_size = 5;  # SELECT MAX(size)

print("<table>");
print("<tr>");
print("<th>");
print("<th>Sizes");

print("<tr>");
print("<th>QTY");
for my $size (1..$max_size) {
   print("<th>$size");
}

my $last_qty;
my $last_size;
for (
   # SELECT qty, size, price ORDER BY qty ASC, size ASC
   [ 100, 1, 43 ],
   [ 100, 2, 45 ],
   [ 100, 3, 50 ],
   [ 200, 4, 55 ],
   [ 250, 1, 52 ],
   [ 250, 2, 55 ],
   [ 250, 3, 56 ],
   [ 250, 5, 61 ],
) {
   my ($size, $qty, $price) = @$_;
   if (!defined($last_qty) || $qty != $last_qty) {
      if (defined($last_size)) {
         print("<td>") for $last_size+1 .. $max_size;
         $last_size = 0;
      }

      print("<tr>");
      print("<th>$qty");
      $last_qty = $qty;
   }

   print("<td>") for $last_size+1 .. $size-1;
   print("<td>\$$price");
}

if (defined($last_size)) {
   print("<td>") for $last_size+1 .. $max_size;
}

print("</table>");
[download]

But it's simpler to just loading everything into memory.

use List::Util qw( max );

my %table;
my $max_size = 0;
for (
   # SELECT qty, size, price
   [ 100, 1, 43 ],
   [ 250, 1, 52 ],
   [ 100, 2, 45 ],
   [ 250, 2, 55 ],
   [ 100, 3, 50 ],
   [ 250, 3, 56 ],
   [ 200, 4, 55 ],
   [ 250, 5, 61 ],
) {
   my ($qty, $size, $price) = @$_;
   $table{$qty}[$size] = $price;
   $max_size = $size if $size > $max_size;
}

print("<table>");
print("<tr>");
print("<th>");
print("<th>Sizes");

print("<tr>");
print("<th>QTY");
for my $size (1..$max_size) {
   print("<th>$size");
}

for my $qty (sort { $a <=> $b } keys(%table)) {
   print("<tr>");
   print("<th>$qty");
   for my $size (1..$num_cols) {
      print("<td>", defined($table{$qty}[$size]) ? "\$$table{$qty}[$si
+ze]" : '');
   }
}

print("</table>");
[download]