在ABAP中使用表达式操作内表（替代READ TABLE）

在传统的ABAP代码中，通常使用READ TABLE来访问某一条内表数据，使用LOOP来访问多条数据。其实，在ABAP中也可以使用表达式的方式来操作内表，以使得代码更简洁。

在本篇博客中，汇总了常用的内表表达式，并给出了与READ TABLE的相对比的写法，供读者参考。
主要包括：

使用内表表达式[ ]访问内表数据；
使用关键在VALUE和BASE为内表赋值；
使用在VALUE关键字中使用FOR实现LOOP循环赋值；
常用的built-in表达式lines_index( )和lines_exist( ).
（1）使用内表表达式[ ]访问内表数据, 索引访问或键值访问。

需要注意的是，在使用表达式的方式访问内表时，若内表内容未找到，并不会给sy-subrc返回值。而是会抛出异常cx_sy_itab_line_not_found。

DATA: lt_sflight TYPE STANDARD TABLE OF sflight,
lt_sflight_sorted TYPE SORTED TABLE OF sflight WITH UNIQUE KEY carrid connid fldate,
ls_sflight TYPE sflight.

SELECT * FROM sflight INTO TABLE lt_sflight WHERE carrid = ‘AA’.
SELECT * FROM sflight INTO TABLE lt_sflight_sorted WHERE carrid = ‘AA’.

• Index access
  READ TABLE lt_sflight INTO ls_sflight INDEX 1.

ls_sflight = lt_sflight[ 1 ].

• key access
  READ TABLE lt_sflight INTO ls_sflight
  WITH KEY carrid = ‘AA’
  connid = ‘0017’.

ls_sflight = lt_sflight[ carrid = ‘AA’ connid = ‘0017’ ].

• table key access
  READ TABLE lt_sflight_sorted INTO ls_sflight
  WITH TABLE KEY carrid = ‘AA’
  connid = ‘0017’
  fldate = ‘20180127’.

ls_sflight = lt_sflight_sorted[ KEY primary_key
COMPONENTS
carrid = ‘AA’
connid = ‘0017’
fldate = ‘20180433’ ].
（2）使用VALUE和BASE为内表赋值

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• Value & Base

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DATA: lt_sflight TYPE STANDARD TABLE OF sflight,
lt_sflight_sorted TYPE SORTED TABLE OF sflight WITH UNIQUE KEY carrid connid fldate,
ls_sflight TYPE sflight.
SELECT * FROM sflight INTO TABLE lt_sflight WHERE carrid = ‘AA’.
SELECT * FROM sflight INTO TABLE lt_sflight_sorted WHERE carrid = ‘AA’.
ls_sflight-carrid = ‘AZ’.
ls_sflight-connid = ‘0788’.
ls_sflight-fldate = ‘20171123’.
APPEND ls_sflight TO lt_sflight.
lt_sflight = VALUE #( ( carrid = ‘AZ’ connid = ‘0788’ fldate = ‘20171123’ ) ).
lt_sflight = VALUE #( BASE lt_sflight
( carrid = ‘AZ’ connid = ‘0788’ fldate = ‘20171123’ )
).
(3) 使用在VALUE关键字中使用FOR实现循环LOOP赋值

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• For expression

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DATA: lt_sflight TYPE STANDARD TABLE OF sflight,
ls_sflight TYPE sflight,
lt_connid_range TYPE RANGE OF sflight-connid,
ls_connid_range LIKE LINE OF lt_connid_range.
SELECT * FROM sflight INTO TABLE lt_sflight WHERE carrid = ‘AA’ OR carrid = ‘AZ’.
LOOP AT lt_sflight INTO ls_sflight WHERE carrid = ‘AZ’.
ls_connid_range-sign = ‘I’.
ls_connid_range-option = ‘EQ’.
ls_connid_range-low = ls_sflight-connid.
ls_connid_range-high = ‘’.
APPEND ls_connid_range TO lt_connid_range.
ENDLOOP.
CLEAR: lt_connid_range.
lt_connid_range = VALUE #( FOR line IN lt_sflight WHERE ( carrid = ‘AZ’ )
( sign = ‘I’ option = ‘EQ’ low = line-connid high = ‘’ )
).
(4) 两个常用的built-in表达式lines_index()和lines_exist.

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• Build-in functions

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DATA: lt_sflight TYPE STANDARD TABLE OF sflight,
ls_sflight TYPE sflight,
lv_index TYPE sy-tabix.
SELECT * FROM sflight INTO TABLE lt_sflight WHERE carrid = ‘AA’ OR carrid = ‘AZ’.

• line_index()
  READ TABLE lt_sflight WITH KEY carrid = ‘AZ’ TRANSPORTING NO FIELDS.
  lv_index = sy-tabix.
  WRITE:/ ‘The index is:’ , lv_index.
  lv_index = line_index( lt_sflight[ carrid = ‘AZ’ ] ).
  WRITE:/ ‘The index is:’ , lv_index.
• line_exist()
  READ TABLE lt_sflight WITH KEY carrid = ‘AZ’ TRANSPORTING NO FIELDS.
  IF sy-subrc = 0.
  WRITE:/ ‘The line exists in itab’.
  ENDIF.
  IF line_exists( lt_sflight[ carrid = ‘AZ’ ] ).
  WRITE:/ ‘The line exists in itab’.
  ENDIF.
• lines( )
  DESCRIBE TABLE lt_sflight LINES lv_lines.
  lv_lines = lines( lt