sap的字段和对象的修改都会保存旧值，数据保存在CDHDR和CDPOS表中，对于提取旧值你可以采用两种方法

 1)使用sap的标准函数CHANGEDOCUMENT_READ_HEADERS 和CHANGEDOCUMENT_READ_POSITIONS

2)使用select语句直接从表中读取。

直接使用SELECT语句读取数据的示例：

*提取信用额度字段修改的抬头信息
      select  cdhdr~changenr cdhdr~udate cdhdr~utime
        into  corresponding fields of table p_cdhdr
        from cdhdr
        where cdhdr~objectclas = 'KLIM' and
          cdhdr~objectid = wa_customerinfo-kunnr.
      if sy-subrc = 0.
*提取信用额度字段修改的字段值
        select cdpos~changenr cdpos~value_old cdpos~value_new
          into corresponding fields of table  p_cdpos
          from cdpos
            for all entries in p_cdhdr
          where cdpos~objectclas = 'KLIM' and
            cdpos~objectid = wa_customerinfo-kunnr and
            cdpos~changenr = p_cdhdr-changenr and
            cdpos~tabname = 'KNKK' and
            cdpos~fname = 'KLIMK'.
        if sy-subrc = 0.
       endif.
endif.