SHIFT  <field_name> LEFT DELETING LEADING 0

Unpacks the packed field A and places it in the field B 
with leading zeros. If B is too  
 short, it is truncated on the left. 
  Example:
  
DATA: p_field (2) TYPE p VALUE 103,
            c_field (8) TYPE c.
UNPACK p_field TO c_field.

WRITE: p_field, c_field.

Output: 103,
        00000103.

To delete leading zeros use PACK.

condense

We can use a function module 'CONVERSION_EXIT_ALPHA_INPUT' 
to add the leading zeros.
example:
 CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'
 EXPORTING
      INPUT = P_KUNNR 
 IMPORTING
      OUTPUT = P_KUNNR.