Datatype mismatch issue between SAP BW and Excel

Hi,

There is a "source system" from which an application extracts and copies data in "excel sheet". This excel sheet is then put in a shared folder from which another application picks it and puts in "destination system". The destination is "BW" and source is "excel". In the source, there is a column called "transaction id" which, at times will have characters, at times numeric and at times alphanumeric. When the data in "transaction id" is numeric and its length is more than 15, the destination system throws out error because excel converts this into scientific format. I am aware that excel has a limitation of treating a number in the scientific format and adding zeros whenever the length of column is more than 15. The target is to save this number in number format only and not in scientific format.

When i talked with the Vendor who handles the destination system, he told me that the datatype that he has put for this column transaction Id is "character" and it has unique key constraint. I found that weird and suggested him to change it to Varchar and use typecasting feature so that this problem doesn't happen again. Yet, he is insisting on me and asking that i need to change it every week manually and then alone send it because there's nothing he can do in destination system which will resolve this issue. I wanted to know if there is any susbtance in his statement or is he ignorant?