calculation in internal table

SELECT

        KONV~KNUMV

        konv~kposn

        konv~kschl

        konv~kbetr as kbetr2

into  CORRESPONDING FIELDS OF TABLE it_display3 from konv

for ALL ENTRIES IN it_display where

               konv~knumv = it_display-knumv AND

               konv~kschl = 'ZCAS'.

LOOP AT it_display.

READ TABLE it_display3 WITH KEY knumv = it_display-knumv . ( You also need to match the KPOSN )

IF sy-subrc = 0.

       it_display-kbetr2 = ( it_display3-kbetr2 / 10 ).

MODIFY it_display.

ENDIF.

ENDLOOP.

I have created another select statement for pr00 as in the above manner.

i wanted to do konv~kschl = PR00 - konv~kschl=ZCAS (PR00 - ZCAS). how to write . I wanted knumv in the selection parameter for this . data should populate based on the selection parameter