sys@mescp> select reverse('123') from dual;REVERSE('123')--------------------------------3211 row selected.sys@mescp> create table test_like as select object_id,object_name from dba_objects;Table created.sys@mescp> create index test_like__name on test_like(object_name);Index created.sys@mescp> create index test_like__name_reverse on test_like(reverse(object_name));Index created.sys@mescp> analyze table test_like compute statistics for table for all indexes;Table analyzed.sys@mescp> set autotrace trace eXPsys@mescp> 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(yōu)化'sys@mescp> 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)sys@mescp> 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 函數(shù)，又可以用上index了'sys@mescp> 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) 新聞熱點
疑難解答
