ประมาณนี้ครับ
1.
Select PatientID, ServiceDate, PressureValue
From Service As a
Where ServiceDate =
(
Select Min(ServiceDate) AS FirstSeviceDateOfYear
From Service As b
Where a.PatientID = b.PatientID
And Year(b.ServiceDate) = 2011
Group By PatientID
)

2.
Select PatientID
From Service
Where Year(ServiceDate) = 2011
Group By PatientID
Having Count(PatientID) > 1

3.
Select PatientID
From Service
Where Year(ServiceDate) = 2011
Group By PatientID
Having Count(PatientID) = 1

-ขอบคุณมากๆๆครับ อาจารย์