(CountCurrent - CountLastMonth) / CountLastMonth

activity, upload_date

SELECT
        Y.CurrentMonth,     Y.CountCurrent,
        Z.LastMonth,  Z.CountLastMonth


 FROM
        (SELECT
        upload_date,
        activity,
            DATE_FORMAT(upload_date,'%M %Y') AS CurrentMonth,
        COUNT(activity) AS CountCurrent
            FROM appmaster
            WHERE activity = 'com.google.test'
            GROUP BY DATE_FORMAT(upload_date,'%m%y'))
    Y INNER JOIN
        (SELECT
        activity,
        DATE_FORMAT(upload_date,'%M %Y') AS CurrentMonth2,
            DATE_FORMAT(upload_date - INTERVAL 1 MONTH,'%M %Y') AS LastMonth,
            COUNT(activity) AS CountLastMonth
        FROM appmaster
        WHERE activity = 'com.google.test'
        GROUP BY DATE_FORMAT(upload_date - INTERVAL 1 MONTH,'%m%y'))
    Z ON Z.CurrentMonth2 = Y.CurrentMonth

GROUP BY DATE_FORMAT(upload_date,'%Y%m')
ORDER BY DATE_FORMAT(upload_date,'%Y%m')

SELECT b.CurrentMonth, sum(b.CountCurrent), b.LastMonth
FROM (SELECT DATE(a.upload_date - INTERVAL 1 MONTH) AS LastMonth, DATE(a.upload_date) AS CurrentMonth, COUNT(a.activity) AS CountCurrent
FROM appmaster a WHERE a.activity = 'com.google.android.googlequicksearchbox'
group BY MONTH(a.upload_date)) AS b

group BY MONTH(b.CurrentMonth)