how to find percentage without calculating manually? - sql

Question

Thanks you for looking.I am new to tsql and dont know how to proceed. I have a table with 10 different companies and 20 department for each(the departments are same for all the companies).
I am trying to calculate percentage of expenses for each department and want an extra column 'Percentage' to be displayed in the result.
please note that for every company the first department is totalcompexpenses which is just the total expenses of the company for all the department combined and dont need to calculate that and should be calculated from the next row.
Is it possible to do this by using while loop or any other way instead of doing it manually for each one of them?
ID |Company_name| Department |Expenses | Percentage
1 |Company1 |TotalComp1Expenses |50000 | -
2 |Company1 |Department1 |4000 | ?
3 |Company1 |Department2 |8000 | ?
4 |Company1 |Department3 |8000 | ?
5 |Company1 |Department4 |7000 | ?
6 |Company1 |Department5 |10000 | ?
...
11 |Company2 |TotalComp2Expenses |100000 | -
12 |Company2 |Department1 |6000 | ?
13 |Company2 |Department2 |5000 | ?
15 |Company2 |Department3 |8000 | ?
15 |Company2 |Department4 |7000 | ?
16 |Company2 |Department5 |10000 | ?
...
21 |Company3 |TotalComp3Expenses |70000 | -
22 |Company3 |Department1 |2000 | ?
23 |Company3 |Department2 |7000 | ?
24 |Company3 |Department3 |9000 | ?
25 |Company3 |Department4 |8000 | ?
26 |Company3 |Department5 |10000 | ?
...

Answer 1

I think the clearest way is to use window functions. If you want the percentages based on the Total% columns, then you can do it as:
select ID, Company_name, Department, Expenses,
(100.0* Expenses /
max(case when Department like 'Total%Expenses' then Expenses end) over
(partition by Company_Name)
) as Percentage
from t;
You can also do this as a sum of the non-Total expenses:
select ID, Company_name, Department, Expenses,
(100.0* Expenses /
max(case when Department not like 'Total%Expenses' then Expenses end) over
(partition by Company_Name)
) as Percentage
from t;
The window function is like an aggregation function, but without the aggregation. The sum for each group is added as an additional column on each row. The definition of the grouping is based on the partition by clause.

Answer 2

Add this column to the query
Expenses * 200.0 / SUM(expenses) over (partition by company_name) as PercentageExepenses
You have to multiply expenses by 200.0 to take into account that you already have the total for the company and therefore double count.

Answer 3

if you self-join and thus have the total of each company in a separate column, you can calculate the percentages. the company total has 100% then, which i deem as correct
select
id
, company_name
, department
, expenses
, expenses/total*100 as percentage
from table_expenses tbx
inner join
(select
company_name
, sum(expenses/2) as expenses
from table_expenses
group by
company_name
) sums
on
(tbx.company_name = sums.company_name)

Answer 4

EDIT:
Are you actually storing the company totals in your database? If, so then this should work for the CTE:
select
compname,
expense as CompExp
from
<YourTable>
where
Department like 'Total%'
But I don't know why you would want to store subtotals like that.
Using your "table" as an example:
;with CompTotal as (
select
compname,
sum(expenses) as CompExp
from
<YourTable>
group by CompName)
select
C.CompName,
Department,
CompTotal.CompExp,
sum(Expenses)as DeptEexpense,
(sum(Expenses) / (CompTotal.CompExp * 1.0)) * 100 as Pct
from
<YourTable> C
inner join
CompTotal
on C.CompName = CompTotal.CompName
group by
C.CompName,
Department,
CompTotal.CompExp
The CTE gives us totals by company. We then join that back to the original table on company name, and total up by Department. Then just regular math gives us the percentage of each department of it's company total.
(SQLFiddle is down, or I'd link to a full example there)