MySQL＃1241-操作数在计数时应包含1列

Question

I am running this query, and I am getting ** #1241 - Operand should contain 1 column(s)** error:

  SELECT `forumCategories`.`id`, `forumCategories`.`name`, `forumCategories`.`order`, `forumCategories`.`description`, `forumCategories`.`date_created`, COUNT(forumPosts.forumCategory_id) as postCount,
    (SELECT `forumPosts`.*, `forumChildPosts`.`id`, `forumChildPosts`.`forumPost_id`, COUNT(forumChildPosts.forumPost_id) as childCount FROM `forumChildPosts` LEFT JOIN `forumPosts` ON `forumPosts`.`id` = `forumChildPosts`.`forumPost_id` GROUP BY `forumPosts`.`id`) AS childCount
    FROM `forumCategories` 
    LEFT JOIN `forumPosts` ON `forumCategories`.`id` = `forumPosts`.`forumCategory_id` 
    GROUP BY `forumCategories`.`id` 
    ORDER BY `forumCategories`.`order` DESC

I have 3 tables:

forumCategories
forumPosts | forumPosts.forumCategory_id = forumCategories.id
forumChildPosts | forumChildPosts.forumPosts_id = forumPosts.id

I want to count all posts for the forum category, and them I want to count all the child posts that belongs to that forum category. How can I do this?

Answer 1

You can't select several items with a subselect and then give them one name. Now you're getting everything from forumPosts, something from forumChildPosts etc and trying to put that into a single column, childCount. This is not allowed.

It might be enough to remove all other result columns from that select and only leave the count ?

Answer 2

I couldn't try it, is that makes sense ? But you can't get nested results from mysql due to its limitation, MYSQL is a Matrix table.

SELECT `forumCategories`.`id`,
       `forumCategories`.`name`,
       `forumCategories`.`order`,
       `forumCategories`.`description`,
       `forumCategories`.`date_created`,
       COUNT(forumPosts.forumCategory_id) AS postCount,
      (SELECT COUNT(forumChildPosts.forumPost_id) AS childCount FROM `forumChildPosts` LEFT JOIN `forumPosts` ON `forumPosts`.`id` = `forumChildPosts`.`forumPost_id` GROUP BY `forumPosts`.`id`) AS childCount
FROM `forumCategories`
LEFT JOIN `forumPosts` ON `forumCategories`.`id` = `forumPosts`.`forumCategory_id`
GROUP BY `forumCategories`.`id`
ORDER BY `forumCategories`.`order` DESC