Fms query in Service Call

Previous Service Call Id :-
Select MAX(Callid) from OSCL T0 where T0.Customer = (Select $[OSCL.customer]) and T0.ItemCode=ItemCode

Previous Service Call Date :-
select mAX(Createdate) from OSCL T0 where T0.internalSN = (Select $[OSCL.internalSN])

Previous Service Call Technician :-
select Top 1 (a.Technician_Name) from OHEM7 a where a.Serial_No = (Select $[OSCL.internalSN])
order by
a.callid desc

Previous Service Call Subject :-
Select Top 1 (b.Subject)  from ohem7 a  inner join OSCL b on a.callid = b.callID
where b.internalSN = (Select $[OSCL.internalSN])
order by
b.callID desc

Previous Service Call Status :-
Select MAX(status) from OSCL T0 where T0.internalSN = (Select $[OSCL.internalSN])

Item Group :-
        if ($[OSCL.Itemgroup]= '201')(SELECT 'Networking')
else if ($[OSCL.Itemgroup]= '102')(SELECT 'Software')

Call Priority :-
        If ($[OSCL.Itemgroup]= '201')(SELECT 'High')
else if ($[OSCL.Itemgroup]= '103')(SELECT 'low')
else if ($[OSCL.Itemgroup]= '112')(SELECT 'Medium')