Creating internal table Using INCLUDE STRUCTURE

Hi Friends,

                   I have a doubt about creating internal table using INCLUDE STRUCTURE .

                   I created a table which has more than 10 fields So i thought to use include structure  but i am getting following error when i am creating

TYPES: BEGIN OF ty_employee.

         INCLUDE STRUCTURE zkarthi_student.

         INCLUDE STRUCTURE zkarthi_marks.

TYPES: END OF ty_employee.

ERROR: Component called MANDT already exists

Both the table ZKARTHI_STUDENT and ZKARTHI_MARKS  has the filed MANDT , how to skip MANDT field alone , ? Is this possible to create an internal which refers the field from two table using INCLUDE STRUCTURE?

                   Please suggest me a best way to solve this problem .