MYSQL加入查询三个表

Question

我需要检索不同的project_name，其中任何worker_id及其supervisor_id为同一个项目工作。我知道答案是bb，dd和ee，但不知道要检索它的查询。这是我目前的查询：

SELECT project.project_name, worker.supervisor_id, projectworker.worker_id
FROM project JOIN projectworker
on project.project_id = projectworker.project_id
JOIN worker
on worker.worker_id = projectworker.worker_id
order by project_name;

检索：

project_name | supervisor_id | worker_id
aa                   4           1
aa                   4           1
aa                   4           2
aa                   4           3
bb                   12          5
bb                   NULL        12
dd                   4           3
dd                   4           6
dd                   3           7
dd                   4           3
ee                   NULL        12
ee                   4           1
ee                   2           8
ee                   1           9
ee                   9           10

Answer 1

这是一种方法。

SELECT project.project_name

FROM   project 

       JOIN projectworker
       on project.project_id = projectworker.project_id

       JOIN worker
       on worker.worker_id = projectworker.worker_id

WHERE  EXISTS (SELECT 1
               FROM   projectworker 
               WHERE  project_id = project.project_id AND worker_id = worker.supervisor_id)

GROUP BY project.project_name

ORDER BY project_name;

Answer 2

试试这个：

SELECT distinct project.project_name, worker.supervisor_id, projectworker.worker_id
FROM project JOIN projectworker
on project.project_id = projectworker.project_id
JOIN worker
on worker.worker_id = projectworker.worker_id
where worker.project_id = projectworker.project_id
order by project_name;