Hello Dennis,
This query should work for your scenario. It will return each domain and the number of installations for software published by Microsoft.
Let me know if you need further help.
Endy
select
a.Domain
,count(su.softwareName) nbrOfInstallations
from tblassets a
Inner Join tblSoftware s On a.AssetID = s.AssetID
Inner Join tblSoftwareUni su On su.SoftID = s.softID
where su.SoftwarePublisher like 'microsoft%'
group by a.Domain