sql - 返回具有最大日期的记录

Question

桌子 -Employee.Status.XREF

Client  Employee    Date
198     Jon Doe     3/1/2009
198     Jon Doe     1/1/2009

桌子 -Employee.Status.History

Client  Employee    Date        Status
198     Jon Doe     5/21/2009   T   
198     Jon Doe     3/1/2009    A
198     Jon Doe     1/1/2009    P

只查询Employee.Status.History和Employee.Status.XREFwhere Client、Employee和Datematch 中的记录。

仅返回Employee.Status.History具有最大日期的记录（按clientby employee）在这种情况下，它将返回

Client  Employee    Date        Status
198     Jon Doe     3/1/2009    A

Answer 1

使用子选择和分组：

select b.*  
from Employee.Status.History b,  
( select client, employee, max(date) date  
  from Employee.Status.XREF  
  group by client, employee  
) a  
where b.client = a.client  
and   b.employee = a.employee  
and   b.date = a.date  

内部查询选择最近的日期。
外部查询返回相关客户和员工在该日期的完整记录。

Answer 2

这应该有效：

SELECT h.*
FROM Employee.Status.History h
INNER JOIN (
    SELECT h.Client, MAX(h.Date) AS MaxDate
    FROM Employee.Status.History h
    INNER JOIN Employee.Status.XREF x ON h.Client = x.Client 
         AND h.Employee = x.Employee AND h.Date = x.Date
) q ON h.Client = q.Client

Answer 3

mysql:

SELECT b.* FROM tableXREF a, tableSTATUS b
WHERE b.client = a.client
ORDER BY b.Date DESC
LIMIT 1

微软的：

SELECT TOP(1) b.field1, b.field2 etc. FROM tableXREF a, tableSTATUS b
WHERE b.client = a.client
ORDER BY b.Date DESC

我猜 ...

Answer 4

为什么不将 join 与 group by 子句一起使用？

select h.client,h.employee,max(h.date),h.Status
from Employee.Status.History h inner join Employee.Status.XREF x on
h.client=x.client and
h.employee=x.employee and
h.date=x.date
group by h.client,h.employee,h.Status