GROUP_CONCAT无法按预期工作

Question

我有很多关系。 Projects表，projects_users表和users表。我正在尝试返回项目列表及其关联用户。这是我正在使用的查询，它可以工作，但只显示一个用户，当我知道应该有更多：

    SELECT
        projects.id,
        `projects`.`project_name`,
        ( GROUP_CONCAT(DISTINCT `users`.`name`  separator ', ' ) ) AS staff,
FROM `projects`
    INNER JOIN `projects_users` ON (`projects_users`.`project_id` = `projects`.`id` )
    INNER JOIN `users` ON (`users`.`id` = `projects_users`.`user_id` ) 
    GROUP BY projects.id, `projects_users`.`user_id` 
    HAVING (`projects_users`.`user_id` = 8)

有几个用户与每个项目相关联，我希望返回类似“用户1，用户2，用户3”的内容。相反，我只得到“用户1”。

Answer 1

由于您需要聚合每个项目的用户，因此您应该根据user_id进行分组：

SELECT
    projects.id,
    `projects`.`project_name`,
    ( GROUP_CONCAT(DISTINCT `users`.`name`  separator ', ' ) ) AS staff
FROM projects -- was missing in the OP
INNER JOIN `projects_users` ON (`projects_users`.`project_id` = `projects`.`id` )
INNER JOIN `users` ON (`users`.`id` = `projects_users`.`user_id` ) 
GROUP BY projects.id -- Group by fixed here
HAVING (`projects_users`.`user_id` = 8)