Question

When I use the following query without LIMIT nested in a subquery

SELECT   `c`.*, 
         GROUP_CONCAT(g.photo SEPARATOR "|") AS `photos_list` 
  FROM   `contests` AS `c` 
              LEFT JOIN 
                  (
                      SELECT   `gallery`.`contest_id`, 
                               `gallery`.`photo` 
                        FROM   `gallery`
                   ) AS `g` ON c.id = g.contest_id 
GROUP BY `c`.`id`

all works fine

id   title    photos_list 

1    title1   50026c35632eb.jpg
2    title2   50026ac53567f.jpg|50026ac5ec82e.jpg|500e71557270f....

Bun when I add LIMIT, I get “photos_list” in only one row. Following query

SELECT   `c`.*, 
         GROUP_CONCAT(g.photo SEPARATOR "|") AS `photos_list` 
  FROM   `contests` AS `c` 
              LEFT JOIN 
                  (
                      SELECT   `gallery`.`contest_id`, 
                               `gallery`.`photo` 
                        FROM   `gallery`
                       LIMIT    0, 2
                   ) AS `g` ON c.id = g.contest_id 
GROUP BY `c`.`id`

will return

id  title   photos_list 

1   title1  NULL
2   title2  50026ac46ea05.jpg|50026ac53567f.jpg

Item with an id = 1 has to contain photos_list, but it doesn’t. Noteworthy that LIMIT does work for item with an id = 2.

What should I do to get a correct result?

Answer 1

SELECT   `c`.*, 
     GROUP_CONCAT(g.photo SEPARATOR "|") AS `photos_list` 
FROM   `contests` AS `c` 
          LEFT JOIN 
              (
                  SELECT   `gallery`.`contest_id`, 
                           `gallery`.`photo` 
                    FROM   `gallery`
               ) AS `g` ON c.id = g.contest_id 
GROUP BY `c`.`id`

Change GROUP_CONCAT to this:

SUBSTRING_INDEX(GROUP_CONCAT(g.photo SEPARATOR "|"),'|',2) AS `photos_list`