SQL selecting rows by most recent date with two unique columns

Using the following query and results, I'm looking for the most recent entry where the ChargeId and ChargeType are unique.

select chargeId, chargeType, serviceMonth from invoice

  	CHARGEID	CHARGETYPE	SERVICEMONTH
1	101		    R		    8/1/2008
2	161		    N	    	2/1/2008
3	101		    R		    2/1/2008
4	101		    R	    	3/1/2008
5	101		    R		    4/1/2008
6	101		    R	    	5/1/2008
7	101		    R	    	6/1/2008
8	101		    R	    	7/1/2008

Desired:

  	CHARGEID	CHARGETYPE	SERVICEMONTH
1	101		    R		    8/1/2008
2	161		    N		    2/1/2008

You can use a GROUP BY to group items by type and id. Then you can use the MAX() Aggregate function to get the most recent service month. The below returns a result set with ChargeId, ChargeType, and MostRecentServiceMonth

SELECT
  CHARGEID,
  CHARGETYPE,
  MAX(SERVICEMONTH) AS "MostRecentServiceMonth"
FROM INVOICE
GROUP BY CHARGEID, CHARGETYPE

So this isn't what the requester was asking for but it is the answer to "SQL selecting rows by most recent date".

Modified from http://wiki.lessthandot.com/index.php/Returning_The_Maximum_Value_For_A_Row

SELECT t.chargeId, t.chargeType, t.serviceMonth FROM( 
    SELECT chargeId,MAX(serviceMonth) AS serviceMonth
    FROM invoice
    GROUP BY chargeId) x 
    JOIN invoice t ON x.chargeId =t.chargeId
    AND x.serviceMonth = t.serviceMonth

SELECT chargeId, chargeType, MAX(serviceMonth) AS serviceMonth 
FROM invoice
GROUP BY chargeId, chargeType

I see most of the developers use inline query without looking out it's impact on huge data.

in simple you can achieve this by:

select a.chargeId, a.chargeType, a.serviceMonth 
from invoice a
left outer join invoice b
on a.chargeId=b.chargeId and a.serviceMonth <b.serviceMonth 
where b.chargeId is null
order by a.serviceMonth desc

select to.chargeid,t0.po,i.chargetype from invoice i
inner join
(select chargeid,max(servicemonth)po from invoice 
group by chargeid)t0
on i.chargeid=t0.chargeid

The above query will work if the distinct charge id has different chargetype combinations.Hope this simple query helps with little performance time into consideration...