Question

Mysql: i need to get the offset of a item in a query.

I have a image gallery: this show 6 image per stack, so when i request image 22 it shows images from 18 to 24. It should first get the offset of the image 22, then get the images from 18 to 24.

Another example: i request the image number 62(and offset 62), it will select images with offset from 60 to 66.

Is possible with a single query?

The main important thing is to get the offset value of the item that has its id equal to a number.

Thanks 😉

EDIT:
select * from images order_by updated_at offset(here i need to get the offset of the image id in this query, and the make some calculation… this is what i need, if is possible.. :d)

EDIT2:
Now I understand that I need 2 queries:

1º: get the offset of the image within the query with my custom order

2º: get the images using the offset from the first query… this I can make it alone, the first one is the problem.. :s

Answer 1

If your images have sequential IDs, you may want to do the following:

SELECT    * 
FROM      images 
WHERE     id >= ((? DIV 6) * 6) AND 
          id < (((? DIV 6) + 1) * 6)
ORDER BY  id;

Replace the ? parameter in the above query with the ID of the image requested.

---

UPDATE: It seems that your images are not ordered by a sequential ID, but by a timestamp. Unfortunately it looks like MySQL does not support variable expressions in the LIMIT clause (Source). One option would be to use a prepared statement:

PREPARE stmt FROM 
" SELECT    * 
  FROM      images
  ORDER BY  updated_at
  LIMIT     ?, 6";

SET @lower_limit := ((22 DIV 6) * 6);

EXECUTE stmt USING @lower_limit;

Another option could be:

SET @row = 0;

SELECT    * 
FROM      images 
WHERE     (@row := @row + 1) BETWEEN ((3 DIV 6) * 6) + 1 and (((3 DIV 6) + 1) * 6)
ORDER BY  updated_at;