Select
HospitalMasterID
,PatientID
,TxnCode
,TxnDate
,PlanDate
,ROW_NUMBER() OVER (PARTITION BY PatientID, PlanDate ORDER BY TxnDate) AS GroupNumber
From Treatments
where PN = 1
Order By PatientID, TxnDate
or probably
SELECT PatientID, PlanDate, Max(GroupNumber) as BenefitCount
FROM (
Select
HospitalMasterID
,PatientID
,TxnCode
,TxnDate
,PlanDate
,ROW_NUMBER() OVER (PARTITION BY PatientID, PlanDate ORDER BY TxnDate) AS GroupNumber
From Treatments
where PN = 1
)
GROUP BY PatientID, PlanDate