如何使用表联接将两个查询联接为一个

Question

这是我的第一个查询，它使用共享相同主键的两个表的表联接：

select s.Branch_ID, count(s.Branch_ID)  'No. of Staff', BranchName 'Branch Name'
from Sales_Staff s , Branch b
where s.Branch_ID = b.Branch_ID
group by s.Branch_ID, BranchName
order by 2 desc

这是第二个查询：

select p.Branch_ID, BranchName, Count(p.Branch_ID) 'Frequency of Packages bought'
from Payment p, Branch b
where p.Branch_ID = b.Branch_ID
Group by p.Branch_ID, BranchName

现在，两者的输出都是我期望和想要的。但是，当我使用相同的方法来连接这两个查询时，数字是错误的。

select p.Branch_ID, BranchName, Count(p.Branch_ID) 'Frequency of Packages bought', count(s.Branch_ID) 'No. of Staff'
from Payment p, Sales_Staff s, Branch b
where p.Branch_ID = s.Branch_ID
and s.Branch_ID = b.Branch_ID
Group by b.Branch_ID, p.Branch_ID, BranchName

错误的输出

任何帮助将不胜感激。

Answer 1

由于您加入的人数越来越多-每个分支机构的每笔付款，每个员工都需要分别进行分组。

select  b.BranchID, b.BranchName, isnull(s.StaffCount,0) as StaffCount, isnull(p.PackageCount,0) as PackageCount
from    Branch b
left join (select Branch_ID, count(*) as StaffCount from SaleStaff group by Branch_ID) s on s.Branch_ID = b.Branch_ID
left join (select Branch_ID, count(*) as PackageCount from Payment group by Branch_ID) p on p.Branch_ID = b.Branch_ID