SQL Addition Formula - sql

Question

Noob alert...
I have an example table as followed.
I am trying to create a column in SQL that shows the what percentage each customer had of size S per year.
So output should be something like:
(Correction: the customer C for 2019 Percentage should be 1)

Answer 1

Window functions will get you there.
DECLARE #TestData TABLE
(
[Customer] NVARCHAR(2)
, [CustomerYear] INT
, [CustomerCount] INT
, [CustomerSize] NVARCHAR(2)
);
INSERT INTO #TestData (
[Customer]
, [CustomerYear]
, [CustomerCount]
, [CustomerSize]
)
VALUES ( 'A', 2017, 1, 'S' )
, ( 'A', 2017, 1, 'S' )
, ( 'B', 2017, 1, 'S' )
, ( 'B', 2017, 1, 'S' )
, ( 'B', 2018, 1, 'S' )
, ( 'A', 2018, 1, 'S' )
, ( 'C', 2017, 1, 'S' )
, ( 'C', 2019, 1, 'S' );
SELECT DISTINCT [Customer]
, [CustomerYear]
, SUM([CustomerCount]) OVER ( PARTITION BY [Customer]
, [CustomerYear]
) AS [CustomerCount]
, SUM([CustomerCount]) OVER ( PARTITION BY [CustomerYear] ) AS [TotalCount]
, SUM([CustomerCount]) OVER ( PARTITION BY [Customer]
, [CustomerYear]
) * 1.0 / SUM([CustomerCount]) OVER ( PARTITION BY [CustomerYear] ) AS [CustomerPercentage]
FROM #TestData
ORDER BY [CustomerYear]
, [Customer];
Will give you
Customer CustomerYear CustomerCount TotalCount CustomerPercentage
-------- ------------ ------------- ----------- ---------------------------------------
A 2017 2 5 0.400000000000
B 2017 2 5 0.400000000000
C 2017 1 5 0.200000000000
A 2018 1 2 0.500000000000
B 2018 1 2 0.500000000000
C 2019 1 1 1.000000000000

Answer 2

Assuming there are no duplicate rows for a customer in a year, you can use window functions:
select t.*,
sum(count) over (partition by year) as year_cnt,
count * 1.0 / sum(count) over (partition by year) as ratio
from t;

Answer 3

Break it apart into tasks - that's probably the best rule to follow when it comes to SQL. So, I created a variable table #tmp which I populated with your sample data, and started out with this query:
select
customer,
year
from #tmp
where size = 'S'
group by customer, year
... this gets a row for each customer/year combo for 'S' entries.
Next, I want the total count for that customer/year combo:
select
customer,
year,
SUM(itemCount) as customerItemCount
from #tmp
where size = 'S'
group by customer, year
... now, how do we get the count for all customers for a specific year? We need a subquery - and we need that subquery to reference the year from the main query.
select
customer,
year,
SUM(itemCount) as customerItemCount,
(select SUM(itemCount) from #tmp t2 where year=t.year) as FullTotalForYear
from #tmp t
where size = 'S'
GROUP BY customer, year
... that make sense? That new line in the ()'s is a subquery - and it's hitting the table again - but this time, its just getting a SUM() over the particular year that matches the main table.
Finally, we just need to divide one of those columns by the other to get the actual percent (making sure not to make it int/int - which will always be an int), and we'll have our final answer:
select
customer,
year,
cast(SUM(itemCount) as float) /
(select SUM(itemCount) from #tmp t2 where year=t.year)
as PercentageOfYear
from #tmp t
where size = 'S'
GROUP BY customer, year
Make sense?

Answer 4

With a join of 2 groupings:
the 1st by size, year, customer and
the 2nd by size, year.
select
t.customer, t.year, t.count, t.size,
ty.total_count, 1.0 * t.count / ty.total_count percentage
from (
select t.customer, t.year, sum(t.count) count, t.size
from tablename t
group by t.size, t.year, t.customer
) t inner join (
select t.year, sum(t.count) total_count, t.size
from tablename t
group by t.size, t.year
) ty
on ty.size = t.size and ty.year = t.year
order by t.size, t.year, t.customer;
See the demo