我有以下问题。看似很简单的一个查询，但我花了那么多时间也没弄明白。
Table ----- project mission craft
project can have many missions, for each mission, it can use multiple air crafts. I want to identify the crafts that was involved with all the missions.
For eg if there are 10 missions, mission 1 can use craft 1 and 2. If there is any craft that used for all the 10 missions (mission 1 -10), that should be output.
I wrote,
select craft,count(mission) from table group by craft
在此之后我不知道如何将这个值与任务总数相匹配。任何帮助将不胜感激。
最佳答案
如果你需要这个用于单个项目，你需要按任务总数过滤工艺任务数:
select c.id from (
select c.id, count(mission_id) cnt
from craft c inner join mission m on (m.id = c.mission_id)
where m.project_id = <project_id>
group by c.id
) as c
where c.cnt = (select count(*) from mission where project_id = <project_id>)
如果所有项目都需要这个:
select c.project_id, c.id from (
select m.project_id, c.id, count(mission_id) cnt
from craft c inner join mission m on (m.id = c.mission_id)
group by m.project_id, c.id
) as c inner join (
select project_id, count(*) cnt
from mission
group by project_id
) as m on (m.project_id = c.project_id)
where c.cnt = m.cnt
关于postgresql - 将总计分组匹配到总计的好方法是什么，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22591913/