Добавяне на проценти към множество преброявания в една SQL SELECT заявка

Можете да използвате подзаявка в from клауза:

select
    s.invalidCount,
    s.unknownCount,
    s.totalCount,
    invalidCount * 100 / s.totalCount as PercentageInvalid,
    unknownCount * 100 / s.totalCount as PercentageUnknown
from
    (select  invalidCount = (SELECT COUNT(*) FROM <...a...> WHERE <...b...>),
        unknownCount = (SELECT COUNT(*) FROM <...c...> WHERE <...d...>),
        totalCount       = (SELECT COUNT(*) FROM <...e...> WHERE <...f...>)) s