Mysql - LEFT JOIN与COUNT

Question

我有2个数据库表

1. 目录
2. directory_category

它们分别通过两个表中的类别ID（作为cat_id和id）链接

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我想列出 directory_category 中的所有类别，同时计算此类别目录中找到的记录数（使用单个SQL查询）< / p>

我试过了

SELECT 
      directory_category.id
      directory_category.category_name
      directory.cat_id
      count(directory) as total_records
      FROM directory_category
      LEFT JOIN directory
      ON directory_category.id = directory.cat_id

此查询仅生成一条记录， total_records 似乎是整个目录表的总和

Answer 1

SELECT 
    directory_category.id,
    directory_category.category_name,
    directory.cat_id,
    COUNT(directory.id) AS total_records
FROM directory_category
LEFT JOIN directory ON directory_category.id = directory.cat_id
GROUP BY directory_category.id

Answer 2

猜测（和快速），我会说：

SELECT 
    directory_category.id,
    directory_category.category_name,
    directory.cat_id,
    count
FROM
    directory_category
LEFT JOIN
    (
        SELECT
            count(directory) as total_records
        FROM
            directory
        INNER JOIN
            directory_category
        ON
            directory_category.id = directory.cat_id
    ) AS count

但显然你需要玩它。