Question

I’m trying to write a query that gives me a percentage (i.e. something like .885, for example) by dividing 2 aggregate numbers I selected via SUM. But my results are coming out as 0.0 instead of the correct number. So just for reference, starting with 2 queries, I have:

SELECT SUM(CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END)
FROM SomeTable

Which yields 158. And:

SELECT SUM(CASE WHEN State_ID = 14 THEN 1 ELSE 0 END)
FROM SomeTable

Yields 203.

Now, if I were to do just this:

SELECT SUM(CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END)/SUM(CASE WHEN State_ID = 14 THEN 1 ELSE 0 END)
FROM SomeTable

I would get 0, because everything is being used as integers. So I tried this:

SELECT CAST(SUM(CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END)/SUM(CASE WHEN State_ID = 14 THEN 1 ELSE 0 END) AS DECIMAL(3,1))
FROM SomeTable

But my result is 0.0. And this is obviously not what I’d like. I’d like to be getting .778

I’m thinking that I need to be casting the numbers individually, but I tried that and got an arithmetic overflow exception. Does anyone see what I could be doing differently?

I’m using SQL Server 2005. Thanks very much.

Answer 1

what happens when you do

THEN 1.0 ELSE 0.0

you can also cast each number that you are dividing, there is no point casting the sum

see also

select 3/2 --1
select 3/2.0 --1.500000
select 3/convert(decimal(3,2),2) --1.500000

So this is one way

SELECT SUM(convert(decimal(3,2),
CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END))/
SUM(convert(decimal(3,2),CASE WHEN State_ID = 14 THEN 1 ELSE 0 END))

To handle division by 0 do this

SELECT CASE SUM(convert(decimal(3,2),CASE WHEN State_ID = 14 THEN 1 ELSE 0 END))
when 0 then 0 else SUM(convert(decimal(3,2),
CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END))/
SUM(convert(decimal(3,2),CASE WHEN State_ID = 14 THEN 1 ELSE 0 END)) END

See also here: SQL Server efficient handling of divide by zero