将数据类型 nvarchar 转换为数字时出错

Question

我的表数据

金额1	金额2	预期结果
100	200	4.17%
一种	500
500	乙
20	100	1.67%

CREATE TABLE [dbo].[tblData](
    [Amount1] [nvarchar](50) NULL,
    [Amount2] [nvarchar](50) NULL
) ON [PRIMARY]

INSERT [dbo].[tblData] ([Amount1], [Amount2]) VALUES (N'100', N'200')
INSERT [dbo].[tblData] ([Amount1], [Amount2]) VALUES (N'A', N'500')
INSERT [dbo].[tblData] ([Amount1], [Amount2]) VALUES (N'', N'')
INSERT [dbo].[tblData] ([Amount1], [Amount2]) VALUES (N'500', N'B')
INSERT [dbo].[tblData] ([Amount1], [Amount2]) VALUES (N'20', N'100')

当我在一行上运行时，这按预期工作正常

SELECT TOP 1
    Concat(CAST((cast(Amount1 AS decimal(18,4))/(cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') AS Result
FROM tblData 

当我在整个桌子上运行时失败

SELECT 
    Concat(CAST((cast(Amount1 AS decimal(18,4))/(cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') AS Result
FROM tblData

返回以下错误消息。

将数据类型 nvarchar 转换为数字时出错

Answer 1

在执行任何操作之前检查列是否为数字：

SELECT Amount1
       , Amount2
       , case when isnumeric(Amount1) = 1 and isnumeric(Amount2) = 1 then
Concat(CAST((cast(Amount1 AS decimal(18,4))/(cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') 
         else 
null
         end AS "Expected Result"
FROM tblData 

这是一个演示

如果您的数据中有 0，则如下所示：

SELECT Amount1, Amount2, 
case when isnumeric(Amount1) = 1 and isnumeric(Amount2) = 1 and Amount2 > 0 and Amount1 > 0 then
Concat(CAST((cast(Amount1 AS decimal(18,4))/(cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') 
when isnumeric(Amount1) = 1 and isnumeric(Amount2) = 1  and Amount1 = 0 and Amount1 > 0 then
Concat(CAST((cast(1 AS decimal(18,4))/(cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') 
when isnumeric(Amount1) = 1 and isnumeric(Amount2) = 1  and Amount1 > 0 and Amount1 = 0 then
Concat(CAST((cast(Amount1 AS decimal(18,4))/(cast(1 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%') 
else 
null
end AS "Expected Result"
FROM tblData 

这是第二个演示

Answer 2

如果你有一个主要是数字的文本字段，但你不能依赖 then 而不是

cast(Amount1 AS decimal(18,4))

你可以使用

try_cast(Amount1 AS decimal(18,4))

如果无法完成转换，则返回 Null

我使用 try_convert 但这只是个人喜好，它们实际上是一样的

try_convert（小数（18,4），金额 1）

所以你的陈述的开头看起来像这样

case 
when try_cast(Amount1 as decimal(18,4))  is not null --Numeric 
and try_cast(Amount2 as decimal(18,4)) > 0 --Numeric and not zero
then Concat(CAST((try_cast(Amount1 AS decimal(18,4))/(try_cast(Amount2 AS decimal(18,4))*12))*100 AS decimal(18,2)),'%')