多个表上的COUNT函数和INNER JOIN

Question

这对我来说太复杂了，因为我通常只使用单表和简单查询（SELECT，INSERT，UPDATE），但现在我处于被卡住的状态。

• 我想要存档的是：当项目经理登录他/她的帐户时，网格视图会显示他/她所有项目的快速概览（ID，创建日期，名称和数量）文件处于待处理状态）如下图：

• 将涉及3个表：

• manager_id = 11的示例数据：

我尝试了这个查询但是没有用，它似乎显示所有列正确但COUNT挂起文件列（假设manager_id = 11）

SELECT COUNT(file_id) as 'Pending files', projects.project_id, projects.project_name, projects.status, projects.start_date
FROM ((project_manager 
INNER JOIN files 
ON project_manager.mag_id = files.manager_id AND project_manager.mag_id = 11 AND file_status = 'Pending')
INNER JOIN projects
ON projects.project_id = project_manager.project_id)
GROUP BY projects.project_id, projects.project_name, projects.status, projects.start_date
ORDER BY projects.status, projects.start_date DESC

• 我的查询结果：

我需要有关正确查询的帮助，如果您能解释一下，我将非常感激！

Answer 1

您需要在Join to the files表中包含project_id并使用左连接 -

SELECT COUNT(file_id) as 'Pending files', projects.project_id, projects.project_name, projects.status, projects.start_date

FROM ((project_manager 
LEFT JOIN files 
ON project_manager.mag_id = files.manager_id AND project_manager.mag_id = 11 AND file_status = 'Pending' AND project_manager.project_Id = files.project_id )
INNER JOIN projects
ON projects.project_id = project_manager.project_id)

WHERE project_manager.mag_id = 11
GROUP BY projects.project_id, projects.project_name, projects.status, projects.start_date
ORDER BY projects.status, projects.start_date DESC