本文章的内容根据SAP系统所带的教程整理而来，查看该性能教程的步骤为：SE38事物代码àEnvironment菜单àExamplesàPerformance Examples
一、 SQL Interface
1. Select ... Where vs. Select + Check
用Select … Where语句效率比Select + Check语句要高，例如：
SELECT * FROM SBOOK INTO SBOOK_WA
WHERE CARRID = 'LH' AND
CONNID = '0400'.
ENDSELECT.
SELECT * FROM SBOOK INTO SBOOK_WA.
CHECK: SBOOK_WA-CARRID = 'LH' AND
SBOOK_WA-CONNID = '0400'.
ENDSELECT.
2. Test Existence
检查满足某个（些）条件的记录是否存在时，使用Select Single效率最高；例如：
SELECT SINGLE * FROM SBOOK
WHERE CARRID = 'LH'.
SELECT * FROM SBOOK INTO SBOOK_WA
WHERE CARRID = 'LH'.
EXIT.
ENDSELECT.
3. Select aggregates
需要对数据库某列求最大，最小，和，平均值或者记录数量时，请使用聚集函数来代替Select … Where + Check的方法，这样效率高而且网络流量小。
DATA: MAX_MSGNR type t100-msgnr.
SELECT MAX( MSGNR ) FROM T100 INTO max_msgnr
WHERE SPRSL = 'D' AND
ARBGB = '00'.
4. Select with select list
取数时请使用Select + 指定的列名称 into，而不要使用Select * into。显示的指定列名称只取出需要的列，不会像Select *会取出相应表的所有的列。
SELECT DOMNAME FROM DD01L
INTO DD01L_WA-DOMNAME
WHERE DOMNAME LIKE 'CHAR%'
AND AS4LOCAL = 'A'.
ENDSELECT.
SELECT * FROM DD01L INTO DD01L_WA
WHERE DOMNAME LIKE 'CHAR%'
AND AS4LOCAL = 'A'.
ENDSELECT.
5. Column Update
尽可能的使用字段（column updates）更新来代替行记录（single-row updates）更新数据库表，这样可以减少网络负载。
UPDATE SFLIGHT
SET SEATSOCC = SEATSOCC - 1.
6. Index and Buffer Support
6.1. Select with index support
Select语句在Where条件中尽量使用索引字段
6.2. Select with buffer support
对于最常用的只读的数据读取，使用SAP Buffering，不要使用BYPASSING BUFFER，例如：
SELECT SINGLE * FROM T100 INTO T100_WA
BYPASSING BUFFER
WHERE SPRSL = 'D'
AND ARBGB = '00'
AND MSGNR = '999'.
7. Array Operations (internal tables)
7.1. Select ... Into Table t
使用Into Table版本的Select 语句要比使用 Append 的方式速度更快，例如：
SELECT * FROM T006 INTO TABLE X006.
DATA T006_WA TYPE T006.
CLEAR X006.
SELECT * FROM T006 INTO T006_WA.
APPEND T006_WA TO X006.
ENDSELECT.
7.2. Array Insert VS Single-row Insert
向数据库中插入数据时，使用内表代替单行操作，减少应用服务与数据库的交互次数，能够有效地减少系统负荷。
INSERT CUSTOMERS FROM TABLE TAB.
LOOP AT TAB INTO TAB_WA.
INSERT INTO CUSTOMERS VALUES TAB_WA.
ENDLOOP.
7.3. Select-Endselect vs. Array-Select
对于只需要使用一次的数据，使用Select-Endselect-loop来代替Select Into
Table。内表需要更多的内存空间。例如：
SELECT * FROM T006 INTO X006_WA.
ENDSELECT.
SELECT * FROM T006
INTO TABLE X006.
LOOP AT X006 INTO X006_WA.
ENDLOOP.
注：个人认为还是取出数据到内表的方式要好，牺牲存储空间，换取时间上的性能。
二、Context
1. Supply/Demand vs. SELECT
三、Internal Tables
1. Using explicit work areas（显示的使用工作区）
显示的指定工作区可以避免不必要的Move操作。见下列内表操作的语句：
APPEND wa TO itab.
INSERT wa INTO itab.
COLLECT wa INTO itab.
MODIFY itab FROM wa.
READ TABLE itab INTO wa.
LOOP AT itab INTO wa.
ITAB = WA.
APPEND ITAB.
2. Linear search vs. binary search
如果内表的数据超过20条，由于线性检索会遍历整个内表，这将会非常耗时。将内表排序并使用Binary Search，或者使用SORTED TABLE类型的内表。如果内表有n条记录，线性查找的次数为O( n )，Binary Search的查找次数为O( log2( n ) ).
READ TABLE ITAB INTO WA WITH KEY K = 'X'
BINARY SEARCH.
READ TABLE ITAB INTO WA
WITH KEY K = 'X'.
3. Dynamic vs. static key access
动态键值的读取比静态键值的读取要慢，
READ TABLE ITAB INTO WA
WITH KEY K = 'X'.
READ TABLE ITAB INTO WA
WITH KEY (NAME) = 'X'.
4. Secondary indices
If you need to access an internal table with different keys repeatedly, keep your own secondary indices. With a secondary index, you can replace a linear search with a binary search plus an index access.
READ TABLE SEC_IDX INTO SEC_IDX_WA
WITH KEY DATE = SY-DATUM
BINARY SEARCH.
IF SY-SUBRC = 0.
READ TABLE ITAB INTO WA
INDEX SEC_IDX_WA-INDX.
" ...
ENDIF.
READ TABLE ITAB INTO WA
WITH KEY DATE = SY-DATUM.
IF SY-SUBRC = 0.
" ...
ENDIF.
5. Key access to multiple lines
LOOP ... WHERE比 LOOP/CHECK更快，因为LOOP ... WHERE只处理满足特定条件的数据。如果LOOP ... WHERE和FROM i1 and/or TO i2条件一起使用，性能会更好。
LOOP AT ITAB INTO WA WHERE K = 'X'.
" ...
ENDLOOP.
LOOP AT ITAB INTO WA.
CHECK WA-K = 'X'.
" ...
ENDLOOP.
6. Sorted and Hashed Tables
6.1. Single Read: Sorted vs. hashed tables
数据在SORTED TABLE类型的内表中按照Binary Search方式组织，检索数据的时间维度为(O (log n))。
数据在HASDED TABLE类型内表中按照hash-algorithm组织，检索数据的时间维度为(O (1))。
HASHED TABLE为单条记录的存取进行了优化，它没有索引(index)，而SORTED TABLE优化为loop操作的部分顺序数据的存取。
DO 250 TIMES.
N = 4 * SY-INDEX.
READ TABLE HTAB INTO WA WITH TABLE KEY K = N.
IF SY-SUBRC = 0.
" ...
ENDIF.
ENDDO.
DO 250 TIMES.
N = 4 * SY-INDEX.
READ TABLE STAB INTO WA WITH KEY K = N.
IF SY-SUBRC = 0.
" ...
ENDIF.
ENDDO.
注：根据实测，Hashed Table的Read Table操作比Sorted Table + Binary Search大约快1倍。
6.2. Part. seq. access: Hashed vs. sorted
Hashed tables优化为单条记录的存取，数据在内表中没有特定的顺序，内表没有索引（
