优化ABAP性能(摘录)

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 statementsSelect 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.

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• 是关于符号的，这点可能注意的人比较少，尽可能用EQ、NE来代替=、<> 等符号，因为用符号的话也会导致读取时效率降低；
•  选用一些替代表/替代字段（VBFA, SHP_IDX_）
  曾做过一些类似于“未拣配交货单”、“未发货过账交货单”的报表，刚开始用的是LIKP、VBUK等表，速度并不理想。后来调试了标准程序VL06O，发现其用的表是SHP_IDX_PICK、SHP_IDX_GDSI等。原来系统在创建交货单的时候，也会更新这些临时表。当拣配完成，该条目就从SHP_IDX_PICK中删除。所以表SHP_IDX_PICK的条目数始终不多，查询速度很快。
  同样的，当我们在多个表中进行查询时，可能不同的限制条件都能达到同样的结果集，但效率差异就很大，所以选用有效的字段非常关键。比如需要查询某销售组织某天已发货的销售订单，我们可以将VBAP与LIPS联查。此时查询条件VBAK-LIFSK=SPACE或VBAP-ABGRU=SPACE并不影响查询结果，但它们可以在第一时间就排除大量无关的订单，对于性能的提升帮助很大。
• 关于表连接语句（INNER JOIN, LEFT JOIN…）

写报表的时候，表与表之间的关联是不可避免的。通常而言，表连接语句要掌握的原则有：
(1)
将最有效的查询条件所对应的表放在第一位。换言之，让查询第一个表后所得到的结果集就尽可能小。
比如有一张报表叫做订单状态统计表，可能查完VBAK、VBAP后还查询LIPS、VTTP等，界面上的查询条件很多。不过据了解得知，该报表主要是查看昨天创建或前几天创建的订单。那么最有效的限制条件自然是订单创建日期，以及销售组织了，而表连接的主表宜选用VBAK。
(2)
确定了表连接的次序后，应考虑将查询条件尽量限制在靠前的表里。比如选择屏幕上有个物料号的查询条件，而我们知道订单VBAP和交货单LIPS均有物料号，那就应该视情况而定，如果表连接中VBAP更早出现，那么WHERE子句中就使用vbap~matnr
IN s_matnr，反之就是lips~matnr IN s_matnr。
(3)
两个表之间进行连接的时候，应考虑关键字段或索引字段的作用。比如查询VTTP和LIPS时，关联关系是vttp~vbeln =
lips~vbeln。那么vttp在前，lips在后，就会比较快，因为根据vttp的vbeln查询lips时，vbeln是lips的关键字段，速度较快。而反过来如果lips在前，那根据lips~vbeln查询vttp会慢一些，除非vbeln是vttp的索引字段。
2，
先构建RANGE再执行SQL语句
有时我们所能用的查询条件不是很理想，比如查询LIKP却必须用公司代码，而非销售组织。
此时普通做法是用LIKP与TVKO根据VKORG进行表联接，从而限制TVKO~BUKRS的值。
还有一种有效的办法是，通过TVKO查询到当期公司代码所对应的全部销售组织，从而组建一个RANGE出来，再根据此RANGE查询LIKP。当然要注意RANGE的行项目有上限的，在ECC6中大概2万行将导致ABAP
DUMP。
提示：DATA r_vkorg TYPE RANGE OF likp-vkorg.
SIGN = ‘I’, OPTION = ‘EQ’,
LOW = ‘XXXX’ 即可往r_vkorg中放入多个单值。