If you use APP ENGINE to report the data from the temp table /staging table on to CSV file using excel format, there is a known issue with fields that have leading zeros. For ex:You have a field of length 6 characters. If the field value is 002123, the excel file removes the leading zeros. But if the requirement is to preserve those leading zeros, we can do something like this.
Update the temp table right before you write out into a file.