从字面看好像作用是相同的，但具体使用以来还是有区别的。如果都是从数据库表中select一次数据，添加到内表中，他们的作用相同；但是多次，他们的作用则有很大差别，INTO TABLE：将数据select出来添加到内表时会将内表先清空再添加，而APPENDING TABLE则会直接追加，实现累计效果。
解释事例：

DATA:BEGIN OF lt_matnr OCCURS 0,
      matnr TYPE mara-matnr,
     END OF lt_matnr.
WRITE :/ '两次INTO TABLE,内表数据：'.
SELECT matnr UP TO 1 ROWS INTO TABLE lt_matnr FROM mara.
SELECT matnr UP TO 1 ROWS INTO TABLE lt_matnr FROM mara.
LOOP AT lt_matnr.
  WRITE:/ lt_matnr-matnr.
ENDLOOP.
REFRESH :lt_matnr.
WRITE :/ '-----------------------------------------------------------'.
WRITE :/ '两次APPENDING TABLE,内表数据：'.
SELECT matnr UP TO 1 ROWS APPENDING TABLE lt_matnr FROM mara.
SELECT matnr UP TO 1 ROWS APPENDING TABLE lt_matnr FROM mara.
LOOP AT lt_matnr.
  WRITE:/ lt_matnr-matnr.
ENDLOOP.

运行结果

Paste_Image.png

实战中的用法：
例如我们预计需新建的表数据会达到亿级别数据，从查询性能的角度考虑，我们需要将表按照一定的数据维度，将表拆分成几个去存储数据。那么在查询是就需要将几张表的数据都放到一个内表中，由于这种场景中多表的结构基本相同，所以使用APPENDING TABLE将会大大简化代码

        SELECT matnr
               lifnr
               werks_d AS werks
               oder_flag
        APPENDING TABLE lt_zpu_matnr
        FROM zpu_matnr_d
        WHERE matnr = ls_mepoitem-matnr
          AND lifnr IN (ls_mepoitem-charg,'')
          AND werks_d = lv_lgort1
          AND datae >= sy-datum
          AND datab <= sy-datum
          AND oder_flag = space
          AND del_flag = space
          AND enable = 'X'.
        SELECT matnr
               lifnr
               werks_d AS werks
               oder_flag
        APPENDING TABLE lt_zpu_matnr
        FROM zpu_matnr_l
        WHERE matnr = ls_mepoitem-matnr
          AND lifnr IN (ls_mepoitem-charg,'')
          AND werks_d = lv_lgort1
          AND datae >= sy-datum
          AND datab <= sy-datum
          AND oder_flag = space
          AND del_flag = space
          AND enable = 'X'.
        SELECT matnr
              lifnr
              werks_s AS werks
              oder_flag
       APPENDING TABLE lt_zpu_matnr
       FROM zpu_matnr_p
       WHERE matnr = ls_mepoitem-matnr
         AND lifnr IN (ls_mepoitem-charg,'')
         AND werks_s = lv_lgort1
         AND datae >= sy-datum
         AND datab <= sy-datum
         AND oder_flag = space
         AND del_flag = space
         AND enable = 'X'.
        SELECT matnr
               lifnr
               werks_s AS werks
               oder_flag
        APPENDING TABLE lt_zpu_matnr
        FROM zpu_matnr_s
        WHERE matnr = ls_mepoitem-matnr
          AND lifnr IN (ls_mepoitem-charg,'')
          AND werks_s = lv_lgort1
          AND datae >= sy-datum
          AND datab <= sy-datum
          AND oder_flag = space
          AND del_flag = space
          AND enable = 'X'.

http://bbs.sapclub.cc/thread-301-1-1.html
(出处: SAP顾问圈)