凡是确切不多多少少mysql

Question

I have one_to_many relationship where i have 3 tables images , items and image_items .. every image may have one or many items, i wanna make a query where i pass the item/items id/ids and get a specific image (exactly one image) based on the count of items inside this image ...

Here is what i have tried so far but it has a problem, it gives me images with that count or more, i'm not sure if this logic or structure is valid in the first place:

SELECT `image_items`.`image_id`
FROM `image_items`
WHERE `image_items`.`item_id` IN(1, 2)
GROUP BY `image_items`.`image_id`
HAVING count(image_items.image_id) = 2 

Here is the fiddle

Lets say image (1) has items (1,2,3), image (2) has items (1,3) and image (3) has items (1,2) .. lets say i want the image that has exactly (1,2) .. with my query even with distinct it gives me images (1,3) when i want only image (3).

Answer 1

Remove the WHERE clause and add in the HAVING clause a condition :

SELECT image_id
FROM image_items
GROUP BY image_id
HAVING 
  COUNT(DISTINCT item_id) = 2 
  AND
  SUM(item_id NOT IN (1, 2)) = 0

See the demo .
Result:

| image_id |
| -------- |
| 4        |

Answer 2

Forpas's solution is a good solution. A slightly simpler having clause is:

SELECT image_id
FROM image_items
GROUP BY image_id
HAVING GROUP_CONCAT(item_id ORDER BY item_id) = '1,2';

If you are constructing this query in an application, this is simpler because you only need to pass in one value, the string '1,2' .

Answer 3

I hope you need to use DISTINCT in the HAVING clause as HAVING COUNT(DISTINCT image_id ) = 2 to get the exact count.

SELECT `image_id`
FROM `image_items`
WHERE `item_id` IN (1, 2)
GROUP BY `image_id`
HAVING COUNT(DISTINCT `image_id`) = 2