如何调整ABAP程序的性能（转）
http://blog.csdn.net/CompassButton/archive/2006/07/31/1004912.aspx
1、使用where语句
不推荐
Select * from zflight.
Check : zflight-airln = ‘LF’ and zflight-fligh = ‘BW222’.
Endselect.
推荐
Select * from zflight where airln = ‘LF’ and fligh = ‘222’.
Endselect.
2、使用聚合函数
不推荐
Maxnu = 0.
Select * from zflight where airln = ‘LF’ and cntry = ‘IN’.
Check zflight-fligh > maxnu.
Maxnu = zflight-fligh.
Endselect.
推荐
Select max( fligh ) from zflight into maxnu where airln = ‘LF’ and cntry = ‘IN’.
3、使用视图代替基本表查询
不推荐
Select * from zcntry where cntry like ‘IN%’.
Select single * from zflight where cntry = zcntry-cntry and airln = ‘LF’.
Endselect.
推荐
Select * from zcnfl where cntry like ‘IN%’ and airln = ‘LF’.
Endselect.
4、使用INTO table 代替select endselect
不推荐
Refresh: int_fligh.
Select * from zflight into int_fligh.
Append int_fligh. Clear int_fligh.
Endselect.
推荐
Refresh: int_fligh.
Select * from zflight into table int_fligh.
5、使用批量修改内表代替逐行修改
不推荐
Loop at int_fligh.
If int_fligh-flag is initial.
Int_fligh-flag = ‘X’.
Endif.
Modify int_fligh.
Endloop.
推荐
Int_fligh-flag = ‘X’.
Modify int_fligh transporting flag where flag is initial.
6、使用二分法查询，提高查询内表数据速度
不推荐
Read table int_fligh with key airln = ‘LF’.
推荐
Read table int_fligh with key airln = ‘LF’ binary search.
7、两个内表添加使用批量增加代替逐行
不推荐
Loop at int_fligh1.
Append int_fligh1 to int_fligh2.
Endloop.
推荐
Append lines of int_fligh1 to int_fligh2.
8、使用table buffering
Use of buffered tables is recommended to improve the performance considerably. The buffer is bypassed while using the following statements
Select distinct
Select … for update
Order by, group by, having clause
Joins
Use the Bypass buffer addition to the select clause in order to explicitly bypass the buffer while selecting the data.
9、 使用FOR ALL Entries
不推荐
Loop at int_cntry.
Select single * from zfligh into int_fligh
where cntry = int_cntry-cntry.
Append int_fligh.
Endloop.
推荐
Select * from zfligh appending table int_fligh
For all entries in int_cntry
Where cntry = int_cntry-cntry.
10、正确地使用where语句，使查询能使用索引
When a base table has multiple indices, the where clause should be in the order of the index, either a primary or a secondary index
To choose an index, the optimizer checks the field names specified in the where clause and then uses an index that has the same order of the fields. One more tip is that if a table begins with MANDT, while an index does not, there is a high possibility that the optimizer might not use that index.
11、正确地使用MOVE语句
Instead of using the move-corresponding clause it is advisable to use the move statement instead. Attempt should be made to move entire internal table headers in a single shot, rather than moving the fields one by one.
12、正确地使用inner join
Let us take an example of 2 tables, zairln and zflight. The table zairln has the field airln, which is the airline code and the field lnnam, which is the name of the airline. The table zflight has the field airln, the airline code and other fields which hold the details of the flights that an airline operates.
Since these 2 tables a re logically joined by the airln field, it is advisable to use the inner join.
Select a~airln a~lnnam b~fligh b~cntry into table int_airdet
From zairln as a inner join zflight as b on a~airln = b~airln.
In order to restrict the data as per the selection criteria, a where clause can be added to the above inner join.
13、使用sort by 代替order by
14、避免使用SELECT DISTINCT语句
使用的 ABAP SORT + DELETE ADJACENT DUPLICATES 代替.
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.
