平时开发过程中遇到一些复杂的逻辑可能避免不了要用双LOOP循环的场景，这种情况下程序的性能是个很大的问题。数据量大一点的程序动辄3-5分钟，更有甚者直接跑到time out。

最近我学习整理了几种双LOOP循环性能优化的方法，在这里记录并分享一下。

首先，我们写一段没有经过优化的双LOOP循环来看看效果。

REPORT test_loop.

TYPES:BEGIN OF ty_a,
        col1(10),
        col2(10),
      END OF ty_a,
      BEGIN OF ty_b,
        col1(10),
        col3(10),
      END OF ty_b,
      BEGIN OF ty_c,
        col1(10),
        col2(10),
        col3(10),
      END OF ty_c.

DATA:wa_a TYPE ty_a,
     wa_b TYPE ty_b,
     wa_c TYPE ty_c,
     gt_a TYPE TABLE OF ty_a,
     gt_b TYPE TABLE OF ty_b,
     gt_c TYPE TABLE OF ty_c.

START-OF-SELECTION.

PERFORM frm_getdata.
PERFORM frm_loop.

FORM frm_getdata.
  DATA lv_line(5) TYPE n.

  DO 5000 TIMES.
    lv_line = sy-index.

    CLEAR wa_a.
    wa_a-col1 = 'col1'&& lv_line.
    wa_a-col2 = 'col2'&& lv_line.
    APPEND wa_a TO gt_a.

    CLEAR wa_b.
    wa_b-col1 = 'col1'&& lv_line.
    wa_b-col3 = 'col3'&& lv_line.
    APPEND wa_b TO gt_b.
  ENDDO.
ENDFORM.

FORM frm_loop.
  DATA lv_t TYPE i.
  GET RUN TIME FIELD DATA(time1).
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b INTO wa_b WHERE col1 = wa_a-col1.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'未经优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.

执行结果：

优化方法1：排序表优化

定义一个排序表并赋值给它，使用排序表进行LOOP循环。

 

FORM frm_loop_sort.
  GET RUN TIME FIELD DATA(time1).
  DATA:gt_b_sort TYPE SORTED TABLE OF ty_b WITH NON-UNIQUE KEY col1.
  SORT gt_b BY col1.
  gt_b_sort[] = gt_b[].
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b_sort INTO wa_b WHERE col1 = wa_a-col1.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  REFRESH gt_c.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'经排序表优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.

执行结果：

 

优化方法2：内表排序INDEX优化

对标准表进行排序并使用INDEX方式进行优化，此方法使用有局限性，要求gt_a-col1不能重复，一旦重复，结果就不对了。

FORM frm_sort_index.
  GET RUN TIME FIELD DATA(time1).
  DATA:i TYPE i.
  SORT:gt_a BY col1,
       gt_b BY col1.
  i = 1.
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b INTO wa_b FROM i.
      IF wa_a-col1 <> wa_b-col1.
        i = sy-tabix.
        EXIT.
      ENDIF.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  REFRESH gt_c.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'经内表排序INDEX优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.

执行结果：

暂时先写这两种优化方法，其它方法后面再继续加。 

 

完整代码：

REPORT test_loop.

TYPES:BEGIN OF ty_a,
        col1(10),
        col2(10),
      END OF ty_a,
      BEGIN OF ty_b,
        col1(10),
        col3(10),
      END OF ty_b,
      BEGIN OF ty_c,
        col1(10),
        col2(10),
        col3(10),
      END OF ty_c.

DATA:wa_a TYPE ty_a,
     wa_b TYPE ty_b,
     wa_c TYPE ty_c,
     gt_a TYPE TABLE OF ty_a,
     gt_b TYPE TABLE OF ty_b,
     gt_c TYPE TABLE OF ty_c,
     lv_t TYPE i.

START-OF-SELECTION.

  PERFORM frm_getdata.
  PERFORM frm_loop.
  PERFORM frm_loop_sort.
  PERFORM frm_sort_index.
  PERFORM frm_hs_group.


FORM frm_getdata.
  DATA lv_line(5) TYPE n.

  DO 5000 TIMES.
    lv_line = sy-index.

    CLEAR wa_a.
    wa_a-col1 = 'col1'&& lv_line.
    wa_a-col2 = 'col2'&& lv_line.
    APPEND wa_a TO gt_a.

    CLEAR wa_b.
    wa_b-col1 = wa_a-col1.
    wa_b-col3 = 'col3'&& lv_line.
    APPEND wa_b TO gt_b.
  ENDDO.
ENDFORM.

FORM frm_loop.
  GET RUN TIME FIELD DATA(time1).
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b INTO wa_b WHERE col1 = wa_a-col1.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  REFRESH gt_c.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'未经优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.

FORM frm_loop_sort.
  GET RUN TIME FIELD DATA(time1).
  DATA:gt_b_sort TYPE SORTED TABLE OF ty_b WITH NON-UNIQUE KEY col1.
  SORT gt_b BY col1.
  gt_b_sort[] = gt_b[].
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b_sort INTO wa_b WHERE col1 = wa_a-col1.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  REFRESH gt_c.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'经排序表优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.

FORM frm_sort_index.
  GET RUN TIME FIELD DATA(time1).
  SORT:gt_a BY col1,
       gt_b BY col1.
  LOOP AT gt_a INTO wa_a.
    LOOP AT gt_b INTO wa_b FROM sy-tabix.
      IF wa_a-col1 <> wa_b-col1.
        EXIT.
      ENDIF.
      wa_c-col1 = wa_a-col1.
      wa_c-col2 = wa_a-col2.
      wa_c-col3 = wa_b-col3.
      APPEND wa_c TO gt_c.
      CLEAR wa_c.
    ENDLOOP.
  ENDLOOP.
  REFRESH gt_c.
  GET RUN TIME FIELD DATA(time2).
  lv_t = time2 - time1.
  WRITE:/'经内表排序INDEX优化，5000条数据执行时间：',lv_t,'微秒'.
ENDFORM.