Sql 选择查询连接选择前1名

我这里有三张表：

DinasHoHeader

，

DinasHoDetail

和

员工

首先我有这个问题

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

正如您所看到的，我得到了重复的

KodeDinasHeader

。我知道这是因为我有不同的

Nip

。因为我只想显示

KodeDinasHeader

和

DepartmentCode

。我正在尝试将我的查询更改为此

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'

我得到的结果是空的。我怎样才能做到这一点

KodeDinasHeader     DepartmentCode
    DN0000007            IT

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。

尝试以下操作：

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。

像这样重写您的查询。请注意，我添加了一个TOP 1，这样您就不需要删除任何列。但是如果你不需要“Nip”列，你可以删除它

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

---

像这样重写您的查询。请注意，我添加了一个TOP 1，这样您就不需要删除任何列。但是如果你不需要“Nip”列，你可以删除它

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

---

当您不需要nip时，为什么要加入表employee？ Nothing表示部门代码属于哪个表

这个呢,

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

---

当您不需要nip时，为什么要加入表employee？ Nothing表示部门代码属于哪个表

这个呢,

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

---

你想用这个做什么？你想要什么结果？你想用这个做什么？你想忘记什么结果。谢谢。没问题，那你能接受答案吗？谢谢。：）我忘了清楚。谢谢。没问题，那你能接受答案吗？谢谢。：）