Taking the record with the max date

The analytic function approach would look something like

SELECT a, some_date_column
  FROM (SELECT a,
               some_date_column,
               rank() over (partition by a order by some_date_column desc) rnk
          FROM tablename)
 WHERE rnk = 1

Note that depending on how you want to handle ties (or whether ties are possible in your data model), you may want to use either the ROW_NUMBER or the DENSE_RANK analytic function rather than RANK.