Question

我在这里有三张表：DinasHoHeader，DinasHoDetail和Employee。

首先我有这个查询

select a.KodeDinasHeader,c.Nip,DepartmentCode 
from DinasHoHeader a 
left join DinasHoDetail b on a.KodeDinasHeader = b.KodeDinasHeader 
left join employee c on b.Nip = c.Nip
where DepartmentCode = 'IT'

我得到了这个结果

KodeDinasHeader   Nip        DepartmentCode
DN0000007       1501971           IT
DN0000007       1411517           IT

正如您所见，我得到重复KodeDinasHeader。我知道这是因为我有不同的Nip。因为我只想展示KodeDinasHeader和DepartmentCode。我正在尝试将查询更改为此

SELECT a.KodeDinasHeader,DepartmentCode From DinasHoHeader a 
left join (
select TOP 1 * from DinasHoDetail
) b on a.KodeDinasHeader = b.KodeDinasHeader
left join employee c on b.Nip = c.Nip
where c.DepartmentCode = 'IT'

我得到空的结果。我怎样才能做到这一点？

KodeDinasHeader     DepartmentCode
    DN0000007            IT

Answer 1

试试这个：

select DISTINCT a.KodeDinasHeader,DepartmentCode 
from DinasHoHeader a 
left join DinasHoDetail b on a.KodeDinasHeader = b.KodeDinasHeader 
left join employee c on b.Nip = c.Nip
where DepartmentCode = 'IT'

注意，我已经添加了DISTINCT并从选择列表中删除了Nip列。

Answer 2

当你不需要压区时，为什么要加入桌面员工呢？ Nothnig表明Dept代码属于哪个表。

这个怎么样，

declare @DeptCode varchar(50)='IT'
select a.KodeDinasHeader,@DeptCode DepartmentCode 
from DinasHoHeader a 
left join DinasHoDetail b on a.KodeDinasHeader = b.KodeDinasHeader -- or inner join
where DepartmentCode = @DeptCode

Answer 3

像这样重写您的查询。请注意，我添加了TOP 1，因此您无需删除任何列。但如果你不需要＆＃34; Nip＆＃34;您可以删除此列

select TOP 1 a.KodeDinasHeader,c.Nip,DepartmentCode 
from DinasHoHeader a 
left join DinasHoDetail b on a.KodeDinasHeader = b.KodeDinasHeader 
left join employee c on b.Nip = c.Nip
where DepartmentCode = 'IT

选择查询连接选择TOP 1

3 个答案: