MySQL查询，我的加入有问题吗？

Question

我不确定这个问题，但看看：

我有 3 张桌子：

1. 类别：ID、图标、名称；
2. 子类别：id、name、description、category_id；
3. 主题：id、title、text、author、created、subcategory_id；

现在我正在尝试获取此信息（查询）：

  $String = "SELECT
  categories.id AS catid,
  categories.icon AS caticon,
  categories.name AS catname,
  subcategories.id AS scatid,
  subcategories.name AS scatname,
  subcategories.description AS scatdescription,
  subcategories.category_id AS scatcatid,
  COUNT(topics.id) AS tid,
  topics.title AS ttitle,
  topics.author AS tauthor,
  topics.created AS tcreated
       FROM
  categories
LEFT JOIN
  subcategories
ON
  subcategories.category_id = 1
LEFT JOIN
  topics
ON
  subcategories.id = topics.subcategory_id
GROUP BY
 categories.id";

结果：

5 中的类别显示 5 - OK， 4 个子类别中的第一个类别仅显示 1 个。

也许查询太长了？感谢您的任何回答。

Answer 1

这个

LEFT JOIN
  subcategories
ON
  subcategories.category_id = 1

应该是这样的

LEFT JOIN
  subcategories
ON
  subcategories.category_id = categories.id