如何调整ABAP程序的性能（续）

15、使用select 字段列表代替 Select *
不推荐
SELECT * FROM DD01L INTO DD01L_WA
  WHERE DOMNAME LIKE 'CHAR%'
        AND AS4LOCAL = 'A'.
ENDSELECT.
推荐
SELECT DOMNAME FROM DD01L
  INTO DD01L_WA-DOMNAME
  WHERE DOMNAME LIKE 'CHAR%'
        AND AS4LOCAL = 'A'.
ENDSELECT.

16、使用subquery代替多个select语句
不推荐
SELECT * FROM SPFLI
  INTO TABLE T_SPFLI
  WHERE CITYFROM = 'FRANKFURT'
    AND CITYTO = 'NEW YORK'.
SELECT * FROM SFLIGHT AS F
    INTO SFLIGHT_WA
    FOR ALL ENTRIES IN T_SPFLI
    WHERE SEATSOCC < F~SEATSMAX
      AND CARRID = T_SPFLI-CARRID
      AND CONNID = T_SPFLI-CONNID
      AND FLDATE BETWEEN '19990101' AND '19990331'.
ENDSELECT.
推荐
SELECT * FROM SFLIGHT AS F INTO SFLIGHT_WA
    WHERE SEATSOCC < F~SEATSMAX
      AND EXISTS ( SELECT * FROM SPFLI
                     WHERE CARRID = F~CARRID
                       AND CONNID = F~CONNID
                       AND CITYFROM = 'FRANKFURT'
                       AND CITYTO = 'NEW YORK' )
      AND FLDATE BETWEEN '19990101' AND '19990331'.
ENDSELECT.

17、如何快速删除重复内表的记录
不推荐
READ TABLE ITAB INDEX 1 INTO PREV_LINE.
LOOP AT ITAB FROM 2 INTO WA.
  IF WA = PREV_LINE.
    DELETE ITAB.
  ELSE.
    PREV_LINE = WA.
  ENDIF.
ENDLOOP.
推荐
DELETE ADJACENT DUPLICATES FROM ITAB
                COMPARING K.

18、如何快速删除内表一定范围内的记录
不推荐
DO 101 TIMES.
  DELETE ITAB INDEX 450.
ENDDO.
推荐
DELETE ITAB FROM 450 TO 550.

19、使用collect语句代替人工合计计算结果
不推荐
LOOP AT ITAB1 INTO WA1.
  READ TABLE ITAB2 INTO WA2 WITH KEY K = WA1-K BINARY SEARCH.
  IF SY-SUBRC = 0.
    ADD: WA1-VAL1 TO WA2-VAL1,
         WA1-VAL2 TO WA2-VAL2.
    MODIFY ITAB2 FROM WA2 INDEX SY-TABIX TRANSPORTING VAL1 VAL2.
  ELSE.
    INSERT WA1 INTO ITAB2 INDEX SY-TABIX.
  ENDIF.
ENDLOOP.
推荐
LOOP AT ITAB1 INTO WA.
  COLLECT WA INTO ITAB2.
ENDLOOP.
SORT ITAB2 BY K.

20、使用显示的work area 代替默认的work area
不推荐
ITAB = WA.
APPEND ITAB.
推荐
APPEND WA TO ITAB.

21、使用LOOP ...ASSIGNING代替loop ... modify.
不推荐（整条记录更新）
LOOP AT ITAB INTO WA.
  I = SY-TABIX MOD 2.
  IF I = 0.
    WA-FLAG = 'X'.
    MODIFY ITAB FROM WA.
  ENDIF.
ENDLOOP.
推荐（只会更新需要修改内容）
LOOP AT ITAB ASSIGNING <WA>.
  I = SY-TABIX MOD 2.
  IF I = 0.
    <WA>-FLAG = 'X'.
  ENDIF.
ENDLOOP.