Calculating ratio only gives 0 or 1?

Question

I have a section of T-SQL code that looks something like this:

select @automation_rate = 
  case 
    when @total_count = 0 then 0
    else @automated_count / @total_count
  end

@automation_rate is decimal(3,2). @total_count and @automated_count are integers.

Unfortunately the only values ever returned for @automation_rate are either 0 or 1. Clearly there is something wrong here, and it may be ridiculously simple, but for the life of me I can't see it.

All data in the underlying resultset (I'm looping over a table) is either 0 or a positive integer. All values are integers except for the automation rate.

Here's example values and expected (using a calculator) vs actual results:

automated count     total count     expected ratio     actual ratio
---------------     -----------     --------------     ------------
              0              35                0.0             0.00
             98             258              37.98             0.00
             74             557              13.29             0.00
            140             140               1.00             1.00

As you can see I get a ratio of 0.00 for all values except where automated = total. I also have an Excel spreadsheet that does the same basic calculation and it comes out perfect (i.e. just like the "expected" column) every time.

So where did I go wrong?

(This is on MS SQL Server 2005, on the off chance that has any impact at all)

Edit Thanks to everyone for the answers. I blew the integer rounding part by assuming since it was moving into a decimal data type that it would automatically convert, instead of realizing it would do the calculation, round, and then convert. Everyone had similar answers so upvotes all around.

Answer 1

This seems to be due to integer math, since @automated_count and @total_count are obviously integers. You need to say:

1.0*@automated_count / @total_count

Or more explicitly:

CONVERT(DECIMAL(5,2), @automated_count) / @total_count

Also these will yield 0.3798 etc. so you might want:

CONVERT(DECIMAL(5,2), 100.0*@automated_count / @total_count)