sql - 将数据类型 nvarchar 转换为数字时出错答案

【问题标题】：sql - Error converting data type nvarchar to numericsql - 将数据类型 nvarchar 转换为数字时出错
【发布时间】：2015-10-28 02:05:58
【问题描述】：

这个查询工作正常

select *  from
(select meas.Inspection_No, case 
when ISNUMERIC(meas.InspectionValue) = 1 then
    cast(meas.InspectionValue as decimal(10,2))
    else 0 End as IVEKVol, meas.InspectionValue,  spec.Name, spec.   [Description], meas.LastDate, meas.ID  from
(select ism.InspectionSpecificationMeasurementID, ism.Name, ism. [Description]  from PT_InspectionSpecification [is]
inner join PT_InspectionSpecification_Measurement ism on   [is].InspectionSpecification_No = ism.InspectionSpecification_No
where [is].PartDescription = 'Anode Dispense' and   [is].InspectionSpecification_type = 'Control Plan' and ism.Name LIKE 'I-IVEKVol    Recorded%') spec
inner join 
PT_InspectionItem_Measurement  meas on  spec.InspectionSpecificationMeasurementID =   meas.InspectionSpecificationMeasurementID) data

但是当我添加 where 子句“where data.IVEKVol > 0”时，我收到错误“将数据类型 nvarchar 转换为数字时出错”

select *  from
(select meas.Inspection_No, case 
when ISNUMERIC(meas.InspectionValue) = 1 then
    cast(meas.InspectionValue as decimal(10,2))
    else 0 End as IVEKVol, meas.InspectionValue,  spec.Name, spec.   [Description], meas.LastDate, meas.ID  from
(select ism.InspectionSpecificationMeasurementID, ism.Name, ism. [Description]  from PT_InspectionSpecification [is]
inner join PT_InspectionSpecification_Measurement ism on   [is].InspectionSpecification_No = ism.InspectionSpecification_No
where [is].PartDescription = 'Anode Dispense' and   [is].InspectionSpecification_type = 'Control Plan' and ism.Name LIKE 'I-IVEKVol    Recorded%') spec
inner join 
PT_InspectionItem_Measurement  meas on  spec.InspectionSpecificationMeasurementID =   meas.InspectionSpecificationMeasurementID) data
where data.IVEKVol > 0

【问题讨论】：

标签： sql sql-server

【解决方案1】：

因为data.IVEKVol列是NVARCHAR类型，所以0是numberic类型

要比较两列，DBMS 必须将两列类型转换为相同类型。

如果data.IVEKVol 列有类似的数据：'1'、'22'、...'' 你可以试试：

WHERE CAST(data.IVEKVol AS INT) > 0  -- Can FOAT, DOUBLE, NUMBERIC, ... instead

如果不是，我认为您的代码如下：

WHERE data.IVEKVol  > N'0' -- recommend
-- OR
WHERE data.IVEKVol  > '0'  -- not recommend

【讨论】：

data.IVEKVol 不是 NVARCHAR，它被转换为小数：当 ISNUMERIC(meas.InspectionValue) = 1 then cast(meas.InspectionValue as decimal(10,2)) else 0 End as IVEKVol