Question

我对SQL甚至是一般的数据库都是新手，所以我不确定这是否是特定于SQL的问题，但无论如何这就是我所拥有的：

3表：

项目

pid
...
finished

Project_Actions

pid
aid

操作

aid
...
finished

如果是必需的信息：

pid = project ID
aid = action ID
One action can belong to >=0 projects

现在，我想在项目表中设置所有相应操作已完成的项目。

我遇到的问题是我完全没有想法，如何在实际更新条目之前检查所有操作。
任何帮助将不胜感激。

Answer 1

您可以选择像这样完成的pid

select p.pid
from projects p
join project_actions pa on pa.pid = p.pid
join actions a on pa.pid = a.pid
group by p.pid
having sum(case when p.finished = 0 then 1 else 0 end) = 0

如果您想更新表格，可以使用

等查询

update projects
set some_column = 'some value'
where pid in
(
   select p.pid
   from projects p
   join project_actions pa on pa.pid = p.pid
   join actions a on pa.pid = a.pid
   group by p.pid
   having sum(case when p.finished = 0 then 1 else 0 end) = 0
)

在MySQL中，您无法更新您选择的同一个表。所以你需要一个像这样的临时表

update projects
set some_column = 'some value'
where pid in
(
   select * from 
   (
     select p.pid
     from projects p
     join project_actions pa on pa.pid = p.pid
     join actions a on pa.pid = a.pid
     group by p.pid
     having sum(case when p.finished = 0 then 1 else 0 end) = 0
   ) tmp
)

SQL迭代结果以检查约束

1 个答案: