Return record with max date

Question

Table – Employee.Status.XREF

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

Table – 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

Only query records in both Employee.Status.History and Employee.Status.XREF where Client , Employee , and Date match.

Return only the record from Employee.Status.History with the max date (by client by employee ) In this case it would return

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

Answer 1

Using a sub-select & group by:

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  

The inner query selects the most recent date.
The outer query returns the entire record on that date for the associated client and employee.

Answer 2

This should work:

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

MsSql:

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

I guess ...

Answer 4

why not use a join with a group by clause?

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