T-SQL 中十进制计算列的精度

Question

我们曾经在数据库中有以下字段：

FieldA    decimal(19, 2)

我们已将该字段更改为计算字段：

ALTER TABLE MyTable
ADD FieldA AS FieldB * FieldC

其中：

FieldB    decimal(19, 2)
FieldC    decimal(19, 5)

由此产生的新的FieldA:

FieldA    (Computed, decimal(38,6))

遗留代码使用 FieldA 并假设它有两位小数。因此，字符串翻译不应用格式。结果，使用新定义，FieldA 显示为六位小数，这是不可接受的。

是否可以修改计算列的精度（例如，保持原始类型 decimal(19, 2)）或者我们是否需要在所有显示值的地方添加适当的格式？

舍入不起作用：

ADD FieldA AS ROUND(FieldB * FieldC, 2)

Answer 1

试试这个：

CREATE TABLE [dbo].[TEST]
(
    [A] DECIMAL(19,2)
   ,[B] DECIMAL(19,5)
   ,[C] AS [A] * [B]
   ,[D] AS CAST([A] * [B] AS DECIMAL(19,2))
);

GO

SELECT *
FROM [sys].[columns]
WHERE [object_id] = OBJECT_ID('[dbo].[TEST]');

为什么？检查 formula 对十进制值执行操作时如何设置小数精度。

所以，我们有：

[A] DECIMAL(19,2)
[B] DECIMAL(19,5)
[C] AS [A] * [B]

公式为：

p1 + p2 + 1 => 2 + 5 + 1 => 7
s1 + s2 => 19 + 19 = > 38

但是：

In multiplication and division operations, we need precision - scale places to store the integral part of the result. The scale might be reduced using the following rules:

The resulting scale is reduced to min(scale, 38 - (precision-scale)) if the integral part is less than 32, because it can't be greater than 38 - (precision-scale). Result might be rounded in this case.

The scale won't be changed if it's less than 6 and if the integral part is greater than 32. In this case, overflow error might be raised if it can't fit into decimal(38, scale)

The scale will be set to 6 if it's greater than 6 and if the integral part is greater than 32. In this case, both integral part and scale would be reduced and resulting type is decimal(38,6). Result might be rounded to 6 decimal places or the overflow error will be thrown if the integral part can't fit into 32 digits.

并且根据规则 3，比例上限为 6，您得到 DECIMAL(38,6)。这就是为什么您需要将结果显式转换为目标十进制类型。

T-SQL 中十进制计算列的精度

Precision of decimal computed columns in T-SQL

tsql

sql-server

decimal

calculated-columns