在對oracle的SQL優化過程中經常會遇到【like'%abc'】破壞索引的問題，但是如果真有此類需求，該如何在不破壞索引的基礎上進行查詢呢。

上程式碼

[email protected]> select reverse('123') from dual;

REVERSE('123')
--------------------------------
321
1 row selected.

[email protected]> create table test_like as select object_id,object_name from dba_objects;

Table created.

 
[email protected]> create index test_like__name on test_like(object_name);

Index created.

[email protected]> create index test_like__name_reverse on test_like(reverse(object_name));

Index created.

[email protected]> analyze table test_like compute statistics for table for all indexes;

Table analyzed.

 
[email protected]> set autotrace trace exp

-- '常量開頭的like , 會利用index ，沒問題…… '

[email protected]> select * from test_like where object_name like AS%';

Execution Plan

----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=655 Bytes=15720)
1 0 TABLE ACCESS (BY INDEX ROWID) OF 'TEST_LIKE' (Cost=2 Card=655Bytes=15720)
2 1 INDEX (RANGE SCAN) OF 'TEST_LIKE__NAME' (NON-UNIQUE) (Cost=2 Card=118)
--'開頭和結尾都是 % ,對不起，很難優化'
 
[email protected]> select * from test_like where object_name like '%%';

Execution Plan

----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=6 Card=655 Bytes=15720)
1 0 TABLE ACCESS (FULL) OF 'TEST_LIKE' (Cost=6 Card=655 ytes=15720)

-- '以常量結束，直接寫的時候是不能應用index的'
[email protected]> select * from test_like where object_name like '%S';
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=6 Card=655 Bytes=15720)

1 0 TABLE ACCESS (FULL) OF 'TEST_LIKE' (Cost=6 Card=655 Bytes=15720)
--'以常量結束的，加個reverse 函式，又可以用上index了'

[email protected]> select * from test_like where reverse(object_name)like reverse('%AS');
Execution Plan

----------------------------------------------------------

0 SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=655 Bytes=15720)
1 0 TABLE ACCESS (BY INDEX ROWID) OF 'TEST_LIKE' (Cost=2 Card=655 Bytes=15720)

2 1 INDEX (RANGE SCAN) OF 'TEST_LIKE__NAME_REVERSE' (NON-UNIQUE) (Cost=2 Card=118)