How to SELECT multiple COUNT(*) columns with each GROUP BY having a different WHERE clause?
This will give you the result you wanted but I'm not sure if it's the most flexible piece of code.

SELECT p.PersonId,
    SUM(CASE 
          WHEN a.ActionTime &gt;= '2014-01-15 00:00:00' 
            AND a.ActionTime &lt; '2014-02-15 00:00:00'
          THEN 1 
          ELSE 0 
        END) AS GroupA_Actions_Made,
    SUM(CASE 
          WHEN a.ActionTime &gt;= '2014-02-15 00:00:00' 
            AND a.ActionTime &lt; '2014-03-15 00:00:00'
          THEN 1 
          ELSE 0 
        END) AS GroupB_Actions_Made
FROM
    Person p
JOIN
    Action a on p.PersonId = a.PersonId
GROUP BY p.PersonId