基本的にこれら 2 つのクエリは、以下のようにサブクエリとして扱います。
select x.number / y.number
from
(
SELECT COUNT(cvu.[ID]) as number, 'Exp' AS [Exp]
FROM [dbo].[tblClientVehicleUnit] cvu
WHERE ExpirationDate < GetDate()
AND cvu.Id = '4C1'
) x
join
(
SELECT COUNT(cvu.[ID]) as number, 'NonExp' AS [Exp]
FROM [dbo].[tblClientVehicleUnit] cvu
WHERE ExpirationDate > GetDate()
AND cvu.Id = '4C1'
) y on 1=1
さらに進めたい場合は、cvu.id を選択の一部として使用し、結合を変更して、すべての cvu.id で実行できるようにすることができます
select x.id, x.number / y.number
from
(
SELECT cvu.id, COUNT(cvu.[ID]) as number, 'Exp' AS [Exp]
FROM [dbo].[tblClientVehicleUnit] cvu
WHERE ExpirationDate < GetDate()
group by cvu.Id
) x
join
(
SELECT cvu.id, COUNT(cvu.[ID]) as number, 'NonExp' AS [Exp]
FROM [dbo].[tblClientVehicleUnit] cvu
WHERE ExpirationDate > GetDate()
group by cvu.Id
)y on x.id = y.id