Sql 需要查看子查询的合并输出

我要看航班号，那次航班的票数，那次航班的工作人员（空姐）数

我可以通过2个子查询查看它们，但无法查看合并视图

        select f.flightid, count(ticketnum)  from flight f , ticket t 
        where f.actDepartDateTime is not null
        and  f.flightid=t.flightid
        group by f.flightid
        order by 1;


        select f.flightid, count(h.staffid) from flight f ,hosting h
        where f.actDepartDateTime is not null
        and   f.flightid=h.flightID 
        group by f.flightid
        order by 1;

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在所有三个表中使用这样一个

内部join

语句

    select f.flightid, 
           count( case when nvl(t.ticketnum,0)>0 then 1 end ) as cnt_ticketnum, 
           count( case when nvl(h.staffid,0)>0   then 1 end ) as cnt_staffid
      from flight f 
      join hosting h on f.flightid=h.flightID 
      join ticket t on f.flightid=t.flightid
     where f.actDepartDateTime is not null           
     group by f.flightid
     order by f.flightid;

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简单解决方案-使用相关子查询进行计数。（无需担心多对多关系、多次加入、无票航班等）

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你也可以使用联合嗨，你可以联合他们！为了理解联合运算符，你需要对h.staffid进行区分，不是吗？非常感谢，我试过了，但不知怎的，计数的正确答案是否定的coming@user2639287不客气。可能您的

t.ticketnum

或

h.staffid

的值为空。因此，我更改了查询。

select f.flightid, 
       (select count(*) from ticket t where f.flightid = t.flightid) as cnt_ticketnum, 
       (select count(*) from hosting h where f.flightid = h.flightID) as cnt_staffid
from flight f 
where f.actDepartDateTime is not null           
order by f.flightid