ABAP区别CLEAR、REFRESH、FREE
CLEAR、REFRESH、FREE
内表：如果使用有表头行的内表，CLEAR 仅清除表格工作区域。
要重置整个内表而不清除表格工作区域，使用REFRESH语句或 CLEAR 语句CLEAR <itab>[].；REFRESH加不加中括号都是只清内表，另外REFRESH是专为清内表的，不能清基本类型变量，但CLEAR可以清基本类型变量。
CLEAR、REFRESH语句都不会释放掉内表所占用的空间。
如果想初始化内表的同时还要释放所占用的空间，请使用：FREE <itab>.
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TYPES: BEGIN OF ty_school,
schoolno(8) TYPE c,
schoolname(20) TYPE c,
END OF ty_school.
DATA gt_school TYPE TABLE OF ty_school WITH HEADER LINE.
gt_school-schoolno = ‘20190001’.
gt_school-schoolname = ‘学生1’.
APPEND gt_school.
CLEAR gt_school.
gt_school-schoolno = ‘20190002’.
gt_school-schoolname = ‘学生2’.
APPEND gt_school.
CLEAR gt_school.
gt_school-schoolno = ‘20190003’.
gt_school-schoolname = ‘学生3’.
INSERT gt_school INDEX 3.
CLEAR gt_school.
WRITE ‘输出全表为：’.
LOOP AT gt_school.
WRITE / gt_school.
ENDLOOP.
gt_school-schoolno = ‘20190003’.
gt_school-schoolname = ‘修改学生3’.
MODIFY gt_school INDEX 3.
CLEAR gt_school.
WRITE / ‘输出全表为：’.
LOOP AT gt_school.
WRITE / gt_school.
ENDLOOP.
CLEAR gt_school.
READ TABLE gt_school WITH KEY schoolno = ‘20190003’.
WRITE: / ‘读取到的行为：’,gt_school.
CLEAR gt_school.
DELETE TABLE gt_school WITH TABLE KEY schoolno = ‘20190003’ schoolname = ‘修改学生3’.
WRITE / ‘删除后的结果为：’.
LOOP AT gt_school.
WRITE / gt_school.
ENDLOOP.
gt_school-schoolno = ‘20190003’.
gt_school-schoolname = ‘修改学生3’.
REFRESH gt_school.
APPEND gt_school.
CLEAR gt_school[].
Free gt_school.
APPEND gt_school.
CLEAR gt_school.
CLEAR gt_school.