在ABAP的SQL语句中写Oracle Hints详解编程语言

①用过的两个写法：

1、指定使用全表扫描：%_HINTS ORACLE FULL(table_name)

2、指定索引：%_HINTS ORACLE INDEX(table_name index_name)

其他Oracle Hints的写法可以参见这篇文章：Oracle Hint的用法

在SQL语句优化过程中，经常会用到hint。

②Using secondary indexes

In the above example, 001 is the secondary index of the table SPFLI. It s a well-known fact that the efficient way of retrieving data from the database tables is by using secondary indexes. Many database vendors provide the optimizer hints for the same. From SAP v4.5, optimizer hints can be provided by the %_HINTS parameter. This is dependent on the database systems that support optimizer hints. The point to be noted here is these optimizer hints are not standardized by the SQL standards. Each database vendor is free to provide the optimizer hints.

Now to know which index to use for our table:

1. Go to SE11 and there specify the table name

2. Now from the menu, goto indexes

3. select the required index.



Now suppose that the identifier 001 represents a non-unique secondary index comprising of the columns CITYFROM and CITYTO. The index name should be defined as:

 tablename ~ Index Identifier 

like SPFLI~001 in the above example.

The sequence of fields in the WHERE condition is of no relevance in using this optimizers index. If you specify hints incorrectly, ABAP ignores them but doesn t return a syntax error or runtime error.

The code was written in R/3 4.6C.




Code



Consider the following example:

REPORT Suresh_test. 

TABLES: spfli. 

DATA : t_spfli LIKE spfli OCCURS 0 WITH HEADER LINE. 

SELECT * FROM spfli 

 INTO TABLE t_spfli 

 %_HINTS ORACLE INDEX("SPFLI" "SPFLI~001"). 

LOOP AT t_spfli. 

 WRITE :/ t_spfli. 

ENDLOOP.

③ABAP--如何在SELECT语句中指定索引(example)

report z_generic_test_program .
 tables: csks.
 start-of-selection.
  select * up to 10 rows from csks
  where kokrs space and
  kostl space
  %_hints oracle index(csks"J").
  write: / csks.
 endselect.  

④Control over FOR ALL ENTRIES Hints 
Under the heading Database Interface Hints, Note 129385 describes the options you have for influencing the database interface by entering hints. The hints are evaluated in the database interface itself and are not passed on to the database. 

Starting with kernel Release 4.6B all the above mentioned FOR ALL ENTRIES parameters can be set via such a hint for a single statement. In the example: 
  SELECT * FROM [..] FOR ALL ENTRIES IN [..] WHERE [..] 
  %_HINTS ORACLE  prefer_in_itab_opt 1 prefer_fix_blocking -1 . 
This way, the boolean parameter prefer_in_itab_opt is explictly set and the boolean parameter prefer_fix_blocking is set to its default value. 

FOR ALL ENTRIES hints, like hints are generally only used as a a corrective device in emergency situations; Note 129385 goes into this. The hints described here should only be used with careful consideration. 

原创文章，作者：ItWorker，如若转载，请注明出处：https://blog.ytso.com/20117.html