执行计算时失去规模

Question

我正在进行计算,但我没有得到预期的答案.我在计算时失去了一些规模.

计算公式为:651/1000*-413.72063274 = -269.33213191(至8 dp)

在SQL Server中我这样做:

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

结果是

result_1:-269.33213200(正确到6dp)
result_2:-269.332132(正确到6dp)

如何获取返回的查询:-269.33213191(正确到8dp)？

Answer 1

对于规则decimal来decimal转换为乘法和除法在BOL描述.

*结果精度和标度的绝对最大值为38.当结果精度大于38时,相应的标度会减小,以防止结果的整数部分被截断.

但是没有详细说明如何进行这种截断.这在此处记录.但有时候只是使用试错法更容易!

以下中间演员表可为您提供所需的结果.你能和那些人住在一起吗？

DECLARE @var NUMERIC(19,8)
DECLARE @a NUMERIC(19,8)
DECLARE @b NUMERIC(19,8)

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

DECLARE @v SQL_VARIANT 
SET @v =  CAST(@a/@b AS NUMERIC(24,10))* CAST(@var AS NUMERIC(23,8))

SELECT    CAST(SQL_VARIANT_PROPERTY(@v, 'BaseType') AS VARCHAR(30)) AS BaseType,    
          CAST(SQL_VARIANT_PROPERTY(@v, 'Precision') AS INT) AS PRECISION,    
          CAST(SQL_VARIANT_PROPERTY(@v, 'Scale') AS INT) AS Scale