Select fields using Rand(1) + Group by "BLOCK"

[Andrei Andrade]

Hello All,

I am getting crazy about this query that I am trying to do.
I have Google it, forums but unfortunately no luck to find the solution.

Let me explain what I am trying to achieve:

I have this table:

+----------+-------------+
|Advert_Id | Advert_Type |
+----------+-------------+
| 1 | 1 |
| 2 | 3 |
| 3 | 1 |
| 4 | 2 |
| 5 | 2 |
| 6 | 3 |
| 7 | 1 |
| 8 | 1 |
| 9 | 1 |
| 10 | 1 |
| 11 | 1 |
| 12 | 1 |
+----------+-------------+

What I need:

Return Rand Advert_Id but ORDER BY Advert_Type IN "BLOCKS" OF 4 (by 3,2,1 and 1)
So, firt block 3,2,1,1 second 3,2,1,1 and so on... if does not have enough records with 3 or 2 it remain the same and return the others.

+----------+-------------+
|Advert_Id | Advert_Type |
+----------+-------------+
| 2 | 3 |
| 4 | 2 |
| 9 | 1 |
| 12 | 1 |
| 6 | 3 |
| 5 | 2 |
| 1 | 1 |
| 8 | 1 |
| 10 | 1 |
| 3 | 1 |
| 11 | 1 |
| 7 | 1 |
+----------+-------------+

Did you understand what I am trying to do? I can do it with PHP using arrays but I was wondering if is possible to do by SQL query?

thanks again,

Andrei