Pay attention to the following points when using append structures

•   You cannot create append structures for pool and cluster tables.
•   If a table contains a long field either of the data type, LCHRor LRAW, you cannot expand the table with an append structure. This is because long fields of this type must always be the last fields in their respective tables. No fields from an append structure may be added after them.
•   If you use an append structure to expand an SAP table, the field names in your append structure must be in the customer namespace, which means they must begin with either YY or ZZ. This prevents naming conflicts from occurring with any new fields that SAP may insert in the future.