How to find out the percentage for alias name this type of query in sql?

Wrap your query with another SELECT. Put all your calculations for percentages in the other SELECT.

SELECT
Rollno, Name,
100 * 'BCOP-201(A)' / 'BCOP-201(D)' P,
...
FROM (
select       Rollno, Name,
      sum(case when scode = 'BCOP-201' then status else 0 end) as 'BCOP-201(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-201') as 'BCOP-201(D)',
      sum(case when scode = 'BCOP-202' then status else 0 end) as 'BCOP-202(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-202') as 'BCOP-202(D)',
      sum(case when scode = 'BCOP-203' then status else 0 end) as 'BCOP-203(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-203') as 'BCOP-203(D)',
      sum(case when scode = 'BCOP-204' then status else 0 end) as 'BCOP-204(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-204') as 'BCOP-204(D)',
      sum(case when scode = 'BCOP-205' then status else 0 end) as 'BCOP-205(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-205') as 'BCOP-205(D)',
      sum(case when scode = 'BCOP-206' then status else 0 end) as 'BCOP-206(A)',
      (select sum(status) from msta where rollno = 777 and scode = 'BCOP-206') as 'BCOP-206(D)'
     
from msta
where rollno <> 777 and doa>=@tfdate and doa<=@ttdate and section='Nil' and semester='Sem-2'
group by rollno, name
) AA


Regards,
Ian

That works fine,
but in the output it suffixs 1,2,3, etc as P, P1,P2 and so on,
the header like this
Rollno,Name,BCOP-201(A),BCOP-201(D),P,BCOP-202(A),BCOP-202(D),P1,BCOP-203(A),BCOP-203(D),P2,BCOP-204(A),BCOP-204(D),P3      BCOP-205(A),BCOP-205(D),P4,BCOP-206(A),BCOP-206(D),P5

Select
Rollno, Name,
[BCOP-201(A)], [BCOP-201(D)], round(([BCOP-201(A)]*100)/[BCOP-201(D)],2) 'P',
[BCOP-202(A)], [BCOP-202(D)], round(([BCOP-202(A)]*100)/[BCOP-202(D)],2) 'P',  
[BCOP-203(A)], [BCOP-203(D)], round(([BCOP-203(A)]*100)/[BCOP-203(D)],2) 'P',
[BCOP-204(A)], [BCOP-204(D)], round(([BCOP-204(A)]*100)/[BCOP-204(D)],2) 'P',  
[BCOP-205(A)], [BCOP-205(D)], round(([BCOP-205(A)]*100)/[BCOP-205(D)],2) 'P',
[BCOP-206(A)], [BCOP-206(D)], round(([BCOP-206(A)]*100)/[BCOP-206(D)],2) 'P'
From (
select       Rollno, Name,
      sum(case when scode = 'BCOP-201' then status else 0 end) as [BCOP-201(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-201') as [BCOP-201(D)],
      sum(case when scode = 'BCOP-202' then status else 0 end) as [BCOP-202(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-202') as [BCOP-202(D)],
      sum(case when scode = 'BCOP-203' then status else 0 end) as [BCOP-203(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-203') as [BCOP-203(D)],
      sum(case when scode = 'BCOP-204' then status else 0 end) as [BCOP-204(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-204') as [BCOP-204(D)],
      sum(case when scode = 'BCOP-205' then status else 0 end) as [BCOP-205(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-205') as [BCOP-205(D)],
      sum(case when scode = 'BCOP-206' then status else 0 end) as [BCOP-206(A)],
      (select sum(status) from mstattendance where rollno = 777 and scode = 'BCOP-206') as [BCOP-206(D)]
     
from mstattendance
where rollno <> 777 and doa>=@tfdate and doa<=@ttdate and section='Nil' and semester='Sem-2'
group by rollno, name) A
end

ok