我有三个表,我想从其中一个表中选择所有数据,并且还会收集在其他两个表中链接特定数据行的次数的COUNT.
所以,从site_projects中选择所有的数据.然后返回一个COUNT的site_project_members WHERE site_projects.id = site_project_members.pid,并返回一个COUNT的site_project_tasks WHERE site_projects.id = site_project_members.pid
我希望我有意义,查询,看起来正确.它会查询数据库(MySQL),没有问题.除了它返回两个计数的总和作为两件事情. (见下表结构)
site_projects
id | title | desc | start | deadline | progress 1 | Project 1 | a project | 1321748906 | 1329847200 | 20
site_project_members
id | pid | uid | img | hidden 1 | 1 | 1 | 1 | 0 2 | 1 | 2 | 2 | 0
site_project_tasks
id | pid | desc | completed 1 | 1 | Task 1 | 1 1 | 1 | Task 2 | 0
这是我的查询：
SELECT p.`id`,p.`title`,p.`desc`,p.`progress`,p.`start`,p.`deadline`,COUNT(m.`id`) as `members`,COUNT(t.`id`) as `tasks` FROM `site_projects` p LEFT JOIN `site_project_members` m ON p.`id`=m.`pid` LEFT OUTER JOIN `site_project_tasks` t ON p.`id`=t.`pid` ORDER BY p.`id` ASC
我得到的结果是：
id | title | desc | progress | start | deadline | members | tasks 1 | Project 1 | a project | 20 | 1321748906 | 1329847200 | 4 | 4
两个“4”值都应该是2.但是它们不是：S任何人都可以帮忙？
非常感激
谢谢,
担
解决方法
SELECT p.id,p.title,p.desc,p.progress,p.start,p.deadline,COALESCE( m.cnt,0 ) AS members,COALESCE( t.cnt,0 ) AS tasks
FROM site_projects p
LEFT JOIN
( SELECT pid,COUNT(*) AS cnt FROM
site_project_members
GROUP BY pid ) m
ON p.id = m.pid
LEFT JOIN
( SELECT pid,COUNT(*) AS cnt FROM
site_project_tasks
GROUP BY pid ) t
ON p.id = t.pid
ORDER BY p.id ASC
