How to calculate third virtual column value based on 2 virtual columns values in sub query

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i have a table named attendance with column named Pre(Bit type) for marking both absent and present.true for present and false for absent i am calculating total classes and attended classes using this column.
now the issue is i cannot think of a way to calculate percentage based on the values in the virtual columns i.e total classes and Attended.
is there any way i can use these column values to calculate percentage in third virtual column named Percentage?

What I have tried:

select distinct s.S_ID,s.Name
 ,(select  count(distinct A_Date) from Attendance
 where  a.C_ID=C_ID ) as Total_Classes,
 (select count(Pre) from Attendance where a.C_ID = C_ID
 and a.S_ID = S_ID and Pre = 'True') as Attended

/* (select count((Pre))/count(distinct A_Date) from Attendance where a.S_ID=S_ID and a.C_ID=C_ID) as Percentage*/
 from Course c full  join StudentCourse sc on c.C_ID = sc.C_ID
 full  join Student s on s.S_ID = sc.S_ID
 full   join Attendance a on a.S_ID = s.S_ID and a.C_ID = c.C_ID where c.C_ID =6

Posted 17-Jun-19 19:10pm

Member 12899279

Updated 21-Jun-19 2:58am

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Member 12899279 · Accepted Answer · 2019-06-21T02:58:00

;with cte as (
select distinct s.S_ID,s.Name
  ,(select  cast(count(distinct A_Date)as float)from Attendance 
  where  a.C_ID=C_ID ) as Total_Classes,
  (select count(Pre) from Attendance where a.C_ID = C_ID 
  and a.S_ID = S_ID and Pre = 'True') as Attended 
  from Course c left outer join StudentCourse sc on c.C_ID = sc.C_ID 
  left outer join Student s on s.S_ID = sc.S_ID 
  left outer  join Attendance a on a.S_ID = s.S_ID and a.C_ID = c.C_ID where c.C_ID=6)
  select *,
  cast(Attended*100/nullif(Total_Classes,0) as decimal(10,2))  Percentage 
  from cte