oracle like模糊查询的优化测试

三种like模糊查询的优化：

第一种：like 'a%'这种，直接可走索引

第二种：like '%a'这种，需要用reverse反转函数改写SQL，再建立函数索引，如下：

改写前:

select * from test where owner like '%SCOTT'

改写后：

select * from test where reverse(owner) like reverse('%SCOTT');

第三种：like '%a%'这种的优化，进行如下测试：

原SQL:

SELECT A0.*

FROM g.wp A0

where A0.ptc_str_12TYPEINFOWABCDT like '%中ABCDdddddddd机%';

OS下执行：

export NLS_LANG=AMERICAN_AMERICA.utf8

SQL> set line 1000

SQL> set pagesize 1000

SQL> set autotrace traceonly

SQL> set timing on

SQL> SELECT A0.*

2 FROM g.wp A0

3 where A0.ptc_str_12TYPEINFOWABCDT like '%中ABCDdddddddd机%';

4694 rows selected.

Elapsed: 00:03:47.72

Execution Plan

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

Plan hash value: 1382574215

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 348K| 330M| 323K (1)| 01:04:46 |

|* 1 | TABLE ACCESS FULL| WABCDT | 348K| 330M| 323K (1)| 01:04:46 |

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

Predicate Information (identified by operation id):

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

1 - filter("A0"."PTC_STR_12TYPEINFOWABCDT" IS NOT NULL AND

"A0"."PTC_STR_12TYPEINFOWABCDT" LIKE '%中ABCDdddddddd机%')

Statistics

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

29 recursive calls

0 db block gets

1292784 consistent gets

39729 physical reads

0 redo size

3087832 bytes sent via SQL*Net to client

52158 bytes received via SQL*Net from client

4696 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

4694 rows processed

为了降低从磁盘中读取数据对查询时间的影响 ，再执行第二次：

SQL> SELECT A0.*

2 FROM g.wp A0

3 where A0.ptc_str_12TYPEINFOWABCDT like '%中ABCDdddddddd机%';

4694 rows selected.

Elapsed: 00:00:33.84

Execution Plan

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

Plan hash value: 1382574215

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 348K| 330M| 323K (1)| 01:04:46 |

|* 1 | TABLE ACCESS FULL| WABCDT | 348K| 330M| 323K (1)| 01:04:46 |

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

Predicate Information (identified by operation id):

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

1 - filter("A0"."PTC_STR_12TYPEINFOWABCDT" IS NOT NULL AND

"A0"."PTC_STR_12TYPEINFOWABCDT" LIKE '%中ABCDdddddddd机%')

Statistics

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

0 recursive calls

0 db block gets

1292776 consistent gets

0 physical reads

0 redo size

3087832 bytes sent via SQL*Net to client

52158 bytes received via SQL*Net from client

4696 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

4694 rows processed

改写SQL:

SELECT A0.*

FROM g.wp A0

where instr(A0.ptc_str_12TYPEINFOWABCDT,'中ABCDdddddddd机')>0;

SQL> SELECT A0.*

2 FROM g.wp A0

3 where instr(A0.ptc_str_12TYPEINFOWABCDT,'中ABCDdddddddd机')>0;

4694 rows selected.

Elapsed: 00:03:36.91

Execution Plan

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

Plan hash value: 1382574215

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 434K| 412M| 323K (1)| 01:04:46 |

|* 1 | TABLE ACCESS FULL| WABCDT | 434K| 412M| 323K (1)| 01:04:46 |

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

Predicate Information (identified by operation id):

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

1 - filter(INSTR("A0"."PTC_STR_12TYPEINFOWABCDT",'中ABCDdddddddd机')>0)

Statistics

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

29 recursive calls

0 db block gets

1292793 consistent gets

39727 physical reads

0 redo size

3087832 bytes sent via SQL*Net to client

52158 bytes received via SQL*Net from client

4696 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

4694 rows processed

建立函数索引：

create index g.fx_WABCDT_1 on g.wp(instr(ptc_str_12TYPEINFOWABCDT,'中ABCDdddddddd机')) tablespace gx parallel 16;

alter index g.fx_WABCDT_1 noparallel;

SQL> SELECT A0.*

2 FROM g.wp A0

3 where instr(A0.ptc_str_12TYPEINFOWABCDT,'中ABCDdddddddd机')>0;

4694 rows selected.

Elapsed: 00:00:02.31

Execution Plan

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

Plan hash value: 3331311615

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 434K| 412M| 12577 (1)| 00:02:31 |

| 1 | TABLE ACCESS BY INDEX ROWID| WABCDT | 434K| 412M| 12577 (1)| 00:02:31 |

|* 2 | INDEX RANGE SCAN | FX_WABCDT_1 | 78135 | | 145 (1)| 00:00:02 |

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

Predicate Information (identified by operation id):

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

2 - access(INSTR("PTC_STR_12TYPEINFOWABCDT",'中ABCDdddddddd机')>0)

Statistics

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

0 recursive calls

0 db block gets

9603 consistent gets

0 physical reads

0 redo size

3085926 bytes sent via SQL*Net to client

52158 bytes received via SQL*Net from client

4696 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

4694 rows processed

逻辑读从 1292776减少到9603，执行时间由33.84s降低到02.31s。但若用绑定变量的情况，不适合这种方法。

若用绑定变量的情况:

指定hint：

SELECT /*+index(A0 CLS_INDEX) */ A0.*

FROM WABCDT A0

where A0.ptc_str_12TYPEINFOWTPART like '中ABCDdddddddd机';

Elapsed: 00:00:05.00

Execution Plan

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

Plan hash value: 4025305430

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 348K| 330M| 141K (1)| 00:28:20 |

| 1 | TABLE ACCESS BY INDEX ROWID| WABCDT | 348K| 330M| 141K (1)| 00:28:20 |

|* 2 | INDEX FULL SCAN | CLS_INDEX | 356K| | 44775 (1)| 00:08:58 |

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

Predicate Information (identified by operation id):

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

2 - filter("A0"."PTC_STR_12TYPEINFOWTPART" IS NOT NULL AND

"A0"."PTC_STR_12TYPEINFOWTPART" LIKE '中ABCDdddddddd机')

Statistics

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

0 recursive calls

0 db block gets

55985 consistent gets

0 physical reads

0 redo size

3085926 bytes sent via SQL*Net to client

52158 bytes received via SQL*Net from client

4696 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

4694 rows processed

上面有用到index full scan，逻辑读减少很多，由1292784减少到55985，若所有需要访问的数据都在内存中，那么执行比较快，上面执行时间为5秒，反之，若需要的数据从磁盘中读取，是比较慢， 所以采用将索引和表的数全部keep到cache中。

先查看db_keep_cache_size大小和索引及表的大小，若keep cache不足以存放表和索引，则需要调大参数。

SQL> show parameter keep

NAME TYPE VALUE

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

buffer_pool_keep string

control_file_record_keep_time integer 7

db_keep_cache_size big integer 15G

SQL> col segment_name for a20;

SQL> select segment_name,segment_type,bytes/1024/1024 "size(MB)" from dba_segments where owner='G' and segment_name in ('WABCDT','CLS_INDEX');

SEGMENT_NAME SEGMENT_TYPE size(MB)

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

WABCDT TABLE 10075

CLS_INDEX INDEX 367

将索引和表keep到内存中：

alter index g.CLS_INDEX storage(buffer_pool keep);

alter table g.wtpart storage(buffer_pool keep);

alter table g.wtpart cache;

SQL> select index_name,buffer_pool from dba_indexes where index_name='CLS_INDEX';

INDEX_NAME BUFFER_

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

CLS_INDEX KEEP

SQL> select owner,table_name,CACHE,BUFFER_POOL from dba_tables where table_name='WABCDT' and owner='G';

OWNER TABLE_NAME CACHE BUFFER_

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

G WABCDT Y KEEP

上面显示已有正确keep表和索引到cache中。这样就可确保除第一次外，其它每次访问的数据都能从内存中获取。

看下count(*)的情况：

SQL> SELECT count(*)

2 FROM WABCDT A0

3 where A0.ptc_str_12TYPEINFOWABCDT like '%中ABCDdddddddd机%';

Elapsed: 00:00:02.04

Execution Plan

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

Plan hash value: 3203503055

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

| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |

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

| 0 | SELECT STATEMENT | | 1 | 11 | 12209 (2)| 00:02:27 |

| 1 | SORT AGGREGATE | | 1 | 11 | | |

|* 2 | INDEX FAST FULL SCAN| CLS_INDEX | 348K| 3742K| 12209 (2)| 00:02:27 |

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

Predicate Information (identified by operation id):

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

2 - filter("A0"."PTC_STR_12TYPEINFOWABCDT" IS NOT NULL AND

"A0"."PTC_STR_12TYPEINFOWABCDT" LIKE '%中ABCDdddddddd机%')

Statistics

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

0 recursive calls

0 db block gets

46773 consistent gets

0 physical reads

0 redo size

527 bytes sent via SQL*Net to client

524 bytes received via SQL*Net from client

2 SQL*Net roundtrips to/from client

0 sorts (memory)

0 sorts (disk)

1 rows processed

上面用了INDEX FAST FULL SCAN，走索引的地方是conut(*),并不是where条件。