Question

I’m performing a calculation and I don’t get the answer I expect. I lose some scale doing the calculation.

Calc is: 651/1000 * -413.72063274 = -269.33213191 (to 8 d.p)

In SQL Server I do this:

declare @var numeric(28,8)
declare @a numeric(28,8)
declare @b numeric(28,8)

set @var = -413.72063274
set @a   = 651.00000000
set @b   = 1000.00000000

select CAST((@a/@b) * @var as numeric(28,8)) as result_1
     , CAST(CAST(@a as numeric(28,8)) 
      /CAST(@b as numeric(28,8)) as numeric(28,8)) 
      *CAST(@var as numeric (28,8))   as result_2

The results is

result_1: -269.33213200 (correct to 6dp)
result_2 : -269.332132 (correct to 6dp)

How do I get the query to return: -269.33213191 (correct to 8dp)?

Answer 1

For this specific case, you could cheat by first multiplying all values and dividing the final result back with this multiplier.

declare @var numeric(28,8)
declare @a numeric(28,8)
declare @b numeric(28,8)
declare @m numeric(28,8)

set @var = -413.72063274
set @a   = 651.00000000
set @b   = 1000.00000000
set @m   = 10000000


select CAST(((@a*@m) * (@var*@m) / (@b*@m)) AS NUMERIC(28, 8)) / @m 
-- Result: -269.3321319137

Edit

on the other hand, following retains its precision without using a multiplier

select CAST(@a * @var AS NUMERIC(28, 8)) / @b
-- Result: -269.3321319140