Question

表格 - Employee.Status.XREF

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

表格 - 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

仅查询Employee.Status.History，Employee.Status.XREF和Client匹配的Employee和Date中的记录。

仅返回Employee.Status.History的记录，其中包含最长日期（client乘以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＆amp;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关联客户端和员工在该日期的整个记录。

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的：

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

MSSQL：

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

为什么不使用group by子句的连接？

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

返回最大日期记录

4 个答案: