casting - SQL Server 2008: Error converting data type nvarchar to float

Question

Presently troubleshooting a problem where running this SQL query:

UPDATE tblBenchmarkData 
SET OriginalValue = DataValue, OriginalUnitID = DataUnitID, 
    DataValue = CAST(DataValue AS float) * 1.335 
WHERE 
    FieldDataSetID = '6956beeb-a1e7-47f2-96db-0044746ad6d5' 
    AND ZEGCodeID IN 
             (SELECT ZEGCodeID FROM tblZEGCode 
              WHERE(ZEGCode = 'C004') OR 
                   (LEFT(ZEGParentCode, 4) = 'C004'))

Results in the following error:

Msg 8114, Level 16, State 5, Line 1
Error converting data type nvarchar to float.

The really odd thing is, if I change the UPDATE to SELECT to inspect the values that are retrieved are numerical values:

SELECT DataValue 
FROM tblBenchmarkData 
WHERE FieldDataSetID = '6956beeb-a1e7-47f2-96db-0044746ad6d5' 
AND ZEGCodeID IN 
         (SELECT ZEGCodeID 
          FROM tblZEGCode WHERE(ZEGCode = 'C004') OR 
                               (LEFT(ZEGParentCode, 4) = 'C004'))

Here are the results:

DataValue
2285260
1205310

Would like to use TRY_PARSE or something like that; however, we are running on SQL Server 2008 rather than SQL Server 2012. Does anyone have any suggestions? TIA.

Answer 1

It would be helpful to see the schema definition of tblBenchmarkData, but you could try using ISNUMERIC in your query. Something like:

SET DataValue = CASE WHEN ISNUMERIC(DataValue)=1 THEN CAST(DataValue AS float) * 1.335 
                     ELSE 0 END