sql-将数据类型nvarchar转换为数值时出错

Question

this query works fine

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

but when i add the where clause "where data.IVEKVol > 0" i get the error "Error converting data type nvarchar to numeric"

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

Answer 1

Because data.IVEKVol column is NVARCHAR type, 0 is numberic type

To compare two columns, DBMS must convert two columns type to a same type.

If data.IVEKVol column have data like: '1', '22',... '' you can try:

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

If not, I think your code like:

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