php - MySQL #1241 - 计数时操作数应包含 1 列

Question

我正在运行此查询，并且收到 ** #1241 - 操作数应包含 1 列** 错误:

  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

我有 3 张 table :

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

我想计算论坛类别的所有帖子，并且我想计算属于该论坛类别的所有子帖子。我怎样才能做到这一点？

Answer 1

您无法使用子选择来选择多个项目，然后为它们指定一个名称。现在，您从forumPosts 获取所有内容，从forumChildPosts 等获取一些内容，并尝试将其放入单个列childCount 中。这是不允许的。

从该选择中删除所有其他结果列并仅保留 count 可能就足够了？