Question

I have a database which holds information about user-created items. Each item can have a number of images associated with it, and I’d like to have an SQL query that 4 random item images, but should not return images from the same item twice.

Here’s a review of the table structures (not full, but including the pertinent information):

Table 1 : item_images:

+----------+--------------+
| item_id  |   filename   |
+----------+--------------+
|    1     |   test.jpg   | 
|    1     |   test2.jpg  |
|    5     |   testy.jpg  |
+----------+--------------+

Table 2: item_link:

+----------+-------------+
| item_id  | category_id |
+----------+-------------+
|    1     |      1      |
|    5     |      1      |
+----------+-------------+

So given the above data, I’d like to return a random image for item # 1 and 5, since they both exist in category # 1.

Here’s the SQL query I have already tried, but for some reason, it always returns the same two images. How might I modify this to return a random image from the matched items?

SELECT `item_images`.`filename` AS `url` FROM `item_images`
  INNER JOIN `item_link` ON `item_images`.`item_id` = `item_link`.`item_id`
  WHERE `item_link`.`category_id` = 1 
  GROUP BY `item_link`.`item_id`
  ORDER BY RAND()
  LIMIT 4

Answer 1

webduos is right distinct should solve your problem

here is explaination

SELECT distinct `item_images`.`filename` AS `url` FROM `item_images`
INNER JOIN `item_link` ON `item_images`.`item_id` = `item_link`.`item_id`
WHERE `item_link`.`category_id` = 1 
GROUP BY `item_link`.`item_id`
ORDER BY RAND()
LIMIT 4