Question

我尝试创建一个连接两个表的视图，并返回截至特定日期的相关地址详细信息。

我有两张桌子：

员工：

ID (Primary key)
Name

EmployeeAddress：

ID (PK), (FK to Employee.ID)
DateValidFrom (PK)
AddressLine1
AddressLine2
PostCode

如何将两者结合起来以获取员工详细信息和某个日期的地址？

Answer 1

您可以使用外部应用：

来执行此操作

select
  E.ID,
  E.Name,
  A.AddressLine1,
  A.AddressLine2,
  A.PostCode
from
  Employee E
  outer apply (
    select top 1
      A.AddressLine1,
      A.AddressLine2,
      A.PostCode
    from
      EmployeeAddress A
    where
      A.ID = E.ID and
      A.DateValidFrom < getdate()
    order by
      A.DateValidFrom desc
  ) A

Answer 2

执行此操作的一种方法是使用查找为每个id找到最新datevalidfrom的查询，并将其用作您加入其他表的派生表，如下所示：

select * from employee e
join employeeaddress ea on e.id = ea.id
join (select id, max(datevalidfrom) as max_date from employeeaddress group by id) ea2
  on ea.id = ea2.id and ea.datevalidfrom = ea2.max_date

通过连接派生表中的max（datevalidfrom），您可以将查询的其余部分（可以获得所有行）限制为最新的。

并将其转变为视图：

create view employee_latest_address as
select e.id, e.name, ea.datevalidfrom, ea.addressline1, ea.addressline2, ea.postcode 
from employee e
join employeeaddress ea on e.id = ea.id
join (select id, max(datevalidfrom) max_date from employeeaddress group by id) ea2
  on ea.id = ea2.id and ea.datevalidfrom = ea2.max_date

使用最新地址记录创建视图

2 个答案: