Many keys in a table

Hi Experts,

Sap receives a segment (idoc) with 15 fields (100 char each). When I analize the next segment, I must know whether the record has been saved before or not.

I can´t save the fields as key in a table because they exceed the limit, and someone suggested me to save them in a table with a guid field and the rest of the fields in the records.

The question is: when the next segment comes, I must calculate the Guid from the fields I have in the segment.

Do you know if there is a way to know the value of the Guid field if I only have the fields?

Please help me out in this.

Thanks in Advance,

Regards,

Liliana.