SQL - percentage using data from case statement

Is there a way of calculating a percentage based on the information returned from a case statement within the SQL? 

I currently have the below case statement, and then a separate static spreadsheet to calculate the percentage of KPI 'pass'. 

Has anyone got examples of SQL that calculate that automatically? 

Thanks in advance (case statement below)

case
when a.job_type_code = 'CL04' and a.actual_comp_date <= b.target_time and a.Photo_Pass = 'Pass' then 'Pass'
when a.job_type_code = 'CL04' and a.actual_comp_date <= (b.target_time + 0.006944444444444) and a.Photo_Pass = 'Pass' then 'Pass'
when a.job_type_code = 'CL04' and a.actual_comp_date is null and sysdate <= (b.target_time + 0.006944444444444) then 'Job open - time remaining'
when a.job_type_code = 'CL04' and a.actual_comp_date is null and sysdate <= (b.target_time + 0.006944444444444) then 'Job open - OVERDUE'

-- All other jobs need to base this on whether they COMPLETED before the target time

when a.job_type_code != 'CL04' and a.actual_on_site <= (b.target_time + 0.006944444444444) and a.Photo_Pass = 'Pass' then 'Pass'
when a.job_type_code != 'CL04' and a.actual_comp_date is null and sysdate <= (b.target_time + 0.006944444444444) then 'Job open - time remaining'
when a.job_type_code != 'CL04' and a.actual_comp_date is null and sysdate <= (b.target_time + 0.006944444444444) then 'Job open - OVERDUE'
when a.job_type_code != 'CL04' and a.actual_on_site <= b.target_time and a.Photo_Pass = 'Pass' then 'Pass'

else 'Fail'
end as KPI_Check,