Count function in gridview

in my gridview query i am using the following query (which was solved by this forum)

SELECT AUTH.company,AUTH.Auth, Count(AUTH.company) AS Held
FROM pers INNER JOIN AUTH ON pers.company = AUTH.company
GROUP BY AUTH.company,AUTH.Auth 

i got the result of above query as under Company   Auth  Held    Sur/Defi Tata           12       02 Dell             11      08 HP               21      20 Opera         11      12 Bangour      10      12 i want one more field as difference between Auth and Held as Sur/Defi