3个条件+随机顺序+分页（Code Igniter + MySQL）

Question

I have a tricky issue to solve, let me see if you can help me...

Im developing a services directory using CodeIgniter + MySQL and, due to my client's business rules, theres 3 plan types. (Platinum, Gold and Silver - in this order from best to worse)

There is a table with the companies tha advertise in the directory, and each one of them may be paying one of this 3 plans.

The problem is:

I have to present the results following this rules: 1. Platinum comes first, than gold, than silver 2. Each range of results MUST BE random itself

Platinum 2
Platinum 1 
Platinum 3 
Gold 3 
Gold 1
GOld 2
Silver 2 
Silver 3
Silver 1

refresh and i get:

Platinum 1
Platinum 3 
Platinum 2 
Gold 2 
Gold 1
GOld 3
Silver 2 
Silver 1
Silver 3

The query in php is something like this:

// after a Select and several joins to filter city, provinces, service types
// i do this to randomize , order and group

        $query = $this->db->order_by('plan.level', 'desc');
        $query = $this->db->order_by('busines.id', 'random');

        $query = $this->db->group_by('business.id'); 
                return $query->result_array();

Until now, so far so good. The problem is, with so many results, i have to paginate them :) How can i do this keeping in mind that:

• The plan priority must be the same through the pages
• the results must be random within the plan "blocks"
• BUT the pagination CANT repeat records through pages or omiss some results

i have to achieve something like this (eg with a 4 per page pagination)

Page I:
Platinum 1
Platinum 4
Platinum 5
Platinum 3

Page II:
Platinum 2
Gold 5
Gold 3
Gold 1

Page III:
Gold 4
Gold 2
Silver 2
Silver 5

Page IV:
Silver 1
Silver 3
Silver 4

and refreshing, randomly changing the position of records INSIDE THE PLAN BLOCKS, within the pages, without repeat or omiss results in the 4 pages, in this example.

Somebody can help me, please. Its a challenge one ;) Thanks, Adriano.

Answer 1

Since the randomization of results has to be preserved across sessions (for pagination), why don't you store in PHP instead of MySQL?

An initial query to get the randomized queries in MySQL:

$this->db->select('id');
// The rest of your ActiveRecord query here, randomized

And perhaps storing the IDs in PHP:

$this->session->set_userdata('random_query', $array_of_random_ids);

Then querying it per page

$array_of_random_ids = $this->session->userdata('random_query');
$this->db->from('business');
$this->db->where_in('id', array_slice($array_of_random_ids, $page_number * $length, $views_per_page);
$this->db->limit($views_per_page, $page_number * $length);

And of course resetting the session later, if that's how you choose to do it.