Count number of Instances of user name if another column is not null

I have a database that stores information on program usage in MySQL.



I use the following query to get the average duration and number of times launched by user name:

SELECT username,
COUNT('username') AS launchcount,
SUBSTRING(SEC_TO_TIME(AVG(TIME_TO_SEC(`durationtime`))), 1, 8) AS averageduration
FROM mcc3dumdb.tbleusage
WHERE 'durationtime' IS NOT Null
Group By username



This works great except for one small problem. It is counting the launch of a username where the duration time is null. The user JBurt should return a count of 4 but it returns 5. How do I modify the above query to only count where a duration time is present? I can tell that it is not averaging where the duration time is null but it is counting it.

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