select st.department, round(avg((sa.normal_salary-sa.dock_salary)),2) as average_actual_salary, if(sum(if(st.staff_gender = 'male',1,0))=0,0.00,round(sum(case when st.staff_gender='male' then (sa.normal_salary-sa.dock_salary) else 0 end)/sum(if(st.staff_gender = 'male',1,0)),2)) as average_actual_sa...