<p>Using the following query and results, I'm looking for the most recent entry where the ChargeId and ChargeType are unique.</p>
<pre><code>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
</code></pre>
<p>Desired:</p>
<pre><code>    CHARGEID    CHARGETYPE  SERVICEMONTH
1   101         R           8/1/2008
2   161         N           2/1/2008
</code></pre>

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
```
```