Long arithmetic with SQL SELECT statement - sql

Question

The basic idea is I have 3 separate SELECT statements that output a number. I need a percentage from those numbers. So the problem would look like this:
(a.count_one + b.count_two) -
(b.count_two + c.count_three) / (a.count_one + b.Count_two) * 100
When I do the code found below I only get the output of the first (a.count_one + b.count_two). BUT if I comment out the third portion which is / (a.count_one + b.count_two) I successfully get the correct solution from (a.count_one + b.count_two) – (b.count_two + c.count_three).
So it appears, doing math of two statements is great, but when I throw in a third statement it pukes and only wants to show the solution of the first problem (a.count_one + b.count_two), but does not even try to calculate the solution for (a.count_one + b.count_two) – (b.count_two + c.count_three) anymore. I'm a bit stumped why.
Select
(a.Count_one + b.Count_two) -
(b.Count_two + c.Count_three) / (a.Count_one + b.Count_two) * 100
as 'Final_Percentage'
from
(
select COUNT(v_Summary.ResourceID) AS Count_one
From [DB1].[dbo].[v_Summary]
) a,
(
select count([CN]) as Count_two
From [DB2].[dbo].[Computers]
WHERE cn NOT IN (SELECT name0 FROM [DB1].[dbo].[v_system] where v_system.Client0 = '1')
) b,
(
select COUNT(v_Summary.ResourceID) AS Count_three
From [DB1].[dbo].[v_Summary]
Where Description like '%/Fail'
) c
And to give additional information. The math problem with numbers:
(54558 + 373) – (373 + 117) / (54558 + 373) * 100
Or further solved:
(54931) - (490) / 55304 * 100 = 98.44%

Answer 1

COUNT function returns int. When you divide two int values the result is again int in SQL Server. So, 490 / 55304 is 0. Then 0 * 100 is 0 again.
Cast the values to a suitable type, like float.
By the way,
(54931) - (490) / 55304 * 100
is not equal to ~98.44, it is equal to ~54930.11399
You need parentheses to get the result you expect:
((54931) - (490)) / 55304 * 100
is equal to ~98.43953421
So, the final query should look like this:
Select
((a.Count_one + b.Count_two) - (b.Count_two + c.Count_three))
/ (a.Count_one + b.Count_two) * 100
as 'Final_Percentage'
from
(
select CAST(COUNT(v_Summary.ResourceID) AS float) AS Count_one
From [DB1].[dbo].[v_Summary]
) a,
(
select CAST(count([CN]) AS float) as Count_two
From [DB2].[dbo].[Computers]
WHERE cn NOT IN (SELECT name0 FROM [DB1].[dbo].[v_system] where v_system.Client0 = '1')
) b,
(
select CAST(COUNT(v_Summary.ResourceID) AS float) AS Count_three
From [DB1].[dbo].[v_Summary]
Where Description like '%/Fail'
) c

Answer 2

You should also get the right result by saying
Select
100.*(a.Count_one - c.Count_three) / (a.Count_one + b.Count_two)
as 'Final_Percentage'
from ... -- unchanged subqueries, as supplied in your question
By moving the *100. right to the front you implicitly convert the first product to float and the type then stays that way for the rest of the calculation. Also, you might have noticed, I simplified the formula, since b.Count_two gets subtracted from itself, so you can leave it out altogether. I have not tested this but I am pretty sure it will work.