Session memory per user

I am building a query to retrieve average session memory per user. So far I cam up with the following:

SELECT s1.username, AVG(s2.value) "avg session memory"
FROM v$session s1
JOIN v$sesstat s2 USING(SID)
JOIN v$statname s3 USING(STATISTIC#)
WHERE s1.TYPE='USER' AND s3.NAME IN('session pga memory','session uga memory') AND s1.username IS NOT NULL
GROUP BY s1.username;

And I just wanted to make sure I am correct and I would appreciate any feedback