MySQL: Fetching Porportionate values for multiple values in select query

Question

This is the table i got with table name photos:

photo_id   user_id
401           1     
403           1     
405           1 
407           2     
408           1     
409           2      
410           1     
411           3      
412           2          
413           2      
420           2      
423           2

I am Currently Using the Query

SELECT *
FROM photos
WHERE user_id
IN ( 1, 2 )
LIMIT 0 , 6

Ids inside IN can have multiple values not just two

What I Get Is

photo_id   user_id
401           1     
403           1     
405           1 
407           2     
408           1     
409           2     

Without Having Proportionate values for each user_id

What I Want is Get Values in Equal Proportion from both UserIds. That is if fetching limit is 6 then i need 3 values or less than 3 if less than 3 elements exists from 1 and 3 values or less than 3 if less than 3 elements exists from 2

And If there are 3 user ids and fetching limit is 6; All three ids will have result with value of 2

photo_id   user_id
401           1     
403           1     
405           1 
407           2     
409           2      
412           2     

I can Do it in Multiple queries ; But Is there any way to do it in single query;

Answer 1

Consider the following...

DROP TABLE IF EXISTS photos;

CREATE TABLE photos
(photo_id   INT NOT NULL PRIMARY KEY
,user_id INT NOT NULL
);

INSERT INTO photos VALUES
(401           ,1),     
(403           ,1),     
(405           ,1),     
(407           ,2),     
(408           ,1),     
(409           ,2),     
(410           ,1),     
(411           ,3),     
(412           ,2),     
(413           ,2),     
(420           ,2),     
(423           ,2);

SELECT x.*
     , COUNT(*) rank 
  FROM photos x 
  JOIN photos y 
    ON y.user_id = x.user_id 
   AND y.photo_id <= x.photo_id 
 GROUP 
    BY x.photo_id
     , x.user_id 
 ORDER 
    BY user_id
     , rank;
+----------+---------+------+
| photo_id | user_id | rank |
+----------+---------+------+
|      401 |       1 |    1 |
|      403 |       1 |    2 |
|      405 |       1 |    3 |
|      408 |       1 |    4 |
|      410 |       1 |    5 |
|      407 |       2 |    1 |
|      409 |       2 |    2 |
|      412 |       2 |    3 |
|      413 |       2 |    4 |
|      420 |       2 |    5 |
|      423 |       2 |    6 |
|      411 |       3 |    1 |
+----------+---------+------+