ABAP内表语法Secondary Keys的用法

在ABAP release 7.0 EhP 2版本后，新增的语法，详细语法请F1，或者Secondary Keys at SAP Help

先分析一段代码：

1. TYPES:ty_vbap TYPE TABLE OF vbap WITH NON-UNIQUE SORTED KEY matnr_werks COMPONENTS matnr werks.
   
2. 
   
3. DATA:t_vbap TYPE ty_vbap.
   
4. DATA:ls_vbap TYPE LINE OF ty_vbap.
   
5. 
   
6. SELECT *
   
7.   UP TO 100 ROWS
   
8.   INTO TABLE t_vbap
   
9.   FROM vbap.
   
10. 
    
11. READ TABLE  t_vbap INTO ls_vbap WITH KEY matnr_werks COMPONENTS matnr = '' werks = ''.
    
12. IF sy-subrc = 0.
    
13. ELSE.
    
14. ENDIF.

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DEBUG视图：

内表T_VBAP有两个键值PRIMARY_KEY和MATNR_WERKS，相当于数据库表中的索引，其中PRIMARY_KEY是所有内表默认的Primary key，MATNR_WERKS就是我们刚才定义内表的Secondary Keys；当执行READ语句时，Secondary Keys数据才会被刷新。

对比两种访问内表的语法区别
1、Standard Access  Access Via Secondary Key

1. * normal access
   
2. *
   
3. READ TABLE t_vbap INTO ls_vbap WITH KEY vbeln = ' ' posnr = ' '.
   
4. 
   
5. LOOP AT t_vbap INTO ls_vbap WHERE vbeln = ' ' AND   posnr = ' '.
   
6. ENDLOOP.
   
7. 
   
8. INSERT LINES OF t_vbap INTO itab INDEX 1.
   
9. 
   
10. APPEND LINES OF t_vbap FROM 1 TO 10 TO itab.
    
11. 
    
12. MODIFY t_vbap FROM ls_vbap TRANSPORTING arktx WHERE vbeln = ' '.
    
13. 
    
14. DELETE t_vbap WHERE vbeln = ' '.

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2、Access Via Secondary Key

1. * Using Secondary Key
   
2. *
   
3. READ TABLE t_vbap INTO ls_vbap WITH KEY matnr_werks COMPONENTS matnr = ' ' werks = ' '.
   
4. 
   
5. LOOP AT t_vbap INTO ls_vbap USING KEY matnr_werks WHERE matnr = ' ' AND   werks = ' '.
   
6. ENDLOOP.
   
7. 
   
8. INSERT LINES OF t_vbap USING KEY matnr_werks INTO itab INDEX 1.
   
9. 
   
10. APPEND LINES OF t_vbap FROM 1 TO 10 USING KEY matnr_werks TO itab.
    
11. 
    
12. MODIFY t_vbap FROM ls_vbap USING KEY matnr_werks TRANSPORTING arktx WHERE matnr = ' ' AND   werks = ' '.
    
13. 
    
14. DELETE t_vbap USING KEY matnr_werks WHERE matnr = ' ' AND   werks = ' '.

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使用注意点：
1、Secondary Keys一般在数据量特别大的内表中才会被使用，Secondary Keys中数据的刷新是需要内表administration进行实时跟踪管理的，会花费一些资源；
2、其次它不适合内表数据经常更改的情况。
除了能声明成排序表，还能声明成哈希表

1. TYPES:ty_vbap TYPE TABLE OF vbap
   
2.               WITH UNIQUE SORTED KEY sort_key COMPONENTS matnr werks
   
3.               WITH NON-UNIQUE SORTED KEY non_sort_key COMPONENTS matnr werks
   
4.               WITH UNIQUE HASHED KEY hash_key COMPONENTS matnr werks.

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NON-UNIQUE 内表中可以有重复数据
UNIQUE 内表中不能有重复数据，否则程序dump

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