SQL Server : new column based on other columns - sql-server

Question

I want to calculate a new value for the new column based on other columns in T-SQL.
My data is look like this:
Each row represents one person in one day.
The WorkHours is calculated based on the Portion column:
Round(FF.Portion * 7.4, 3) AS WorkHours
I want to calculate a percentage of hours which people not have been at work in relation to the TOTAL workhours for day for each school. For example if 10 people work full hour in one school for one day, it gives 74 working hours and if one person have been sick that day it will give (7,4 % 74 * 100) which is 10% (the WorkHours is calculated based on Portion column)

Answer 1

In your comment you state Peter had 6 hours on 1/1/2017 as "seek" but it was actually 7.4. With that in mind, we can calculate your results as follows:
declare #table table (Name varchar(16), Date date, School char(2), FreedayCode int, Freeday varchar(64), Portion decimal (6,4))
insert into #table
values
('Mike','20170101','AA',-1,'AtWork',1),
('Mike','20170201','AA',1,'Seek',1),
('Ali','20170101','BB',-1,'AtWork',0.94594),
('Ali','20170201','BB',-1,'AtWork',0.94594),
('Sara','20170101','CC',2,'holiday',1),
('Sara','20170201','CC',1,'Seek',1),
('Peter','20170101','AA',1,'Seek',1),
('Peter','20170201','AA',1,'Seek',1),
('Nina','20170101','AA',-1,'AtWork',0.81081),
('Nina','20170201','AA',-1,'AtWork',0.81081)
select
Name
,Date
,School
,FreeDayCode
,Freeday,Portion
,NewColumn = sum(case when Freeday <> 'AtWork' then Round(Portion * 7.4,3) else 0 end) over (partition by Date, School) / sum(Round(Portion * 7.4,3)) over (partition by Date, School)
from
#table
order by
Date
,School
RETURNS
+-------+------------+--------+-------------+---------+---------+-----------+
| Name | Date | School | FreeDayCode | Freeday | Portion | NewColumn |
+-------+------------+--------+-------------+---------+---------+-----------+
| Mike | 2017-01-01 | AA | -1 | AtWork | 1.0000 | 0.355769 |
| Peter | 2017-01-01 | AA | 1 | Seek | 1.0000 | 0.355769 |
| Nina | 2017-01-01 | AA | -1 | AtWork | 0.8108 | 0.355769 |
| Ali | 2017-01-01 | BB | -1 | AtWork | 0.9459 | 0.000000 |
| Sara | 2017-01-01 | CC | 2 | holiday | 1.0000 | 1.000000 |
| Peter | 2017-02-01 | AA | 1 | Seek | 1.0000 | 0.711538 |
| Mike | 2017-02-01 | AA | 1 | Seek | 1.0000 | 0.711538 |
| Nina | 2017-02-01 | AA | -1 | AtWork | 0.8108 | 0.711538 |
| Ali | 2017-02-01 | BB | -1 | AtWork | 0.9459 | 0.000000 |
| Sara | 2017-02-01 | CC | 1 | Seek | 1.0000 | 1.000000 |
+-------+------------+--------+-------------+---------+---------+-----------+