How do I get minimum date

Declare @dateDate as DateTime
Set @dateDate = SYSDATETIME()

select distinct a.PatientName,
       a.PatientSSN,
       CONVERT(Date, @dateDate) AS FIRSTVISIT
from    SPatient.SPatient as a
    JOIN OUTPAT.VISIT AS D
        ON A.PATIENTSID=D.PATIENTSID
    join Dim.Location as c
        on D.LocationSID=c.LocationSID
where c.locationname like '%wi-%'
      and c.LocationName not like '%wi-PHONE%'
      and c.LocationName not like '%non va%'
      and c.LocationName not like '%ds%'
group by a.patientname, a.patientssn
order by a.patientname, a.patientssn