MySQL 查询，我的连接有问题吗？

Question

我不确定这个问题，但看看:

我有 3 张 table :

1. 类别:ID、图标、名称；
2. 子类别:id、名称、描述、category_id；
3. 主题:id、标题、文本、作者、创建、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:

类别从 5 显示 5 - 好的， 4 个子类别仅在第一类别中显示 1 个。

也许查询太长？感谢您的回答。

Answer 1

这个

LEFT JOIN
  subcategories
ON
  subcategories.category_id = 1

应该是这个

LEFT JOIN
  subcategories
ON
  subcategories.category_id = categories.id