SQL> create table test as select * from dba_objects;

表已創建。

SQL> select owner,object_name from test where owner like 'ROBINSON%';

OWNER??????????????????????????????????????????????????????? OBJECT_NAME
------------------------------------------------------------ ------------------------------
ROBINSON???????????????????????????????????????????????????? TEST
ROBINSON???????????????????????????????????????????????????? T2
ROBINSON???????????????????????????????????????????????????? T1
ROBINSON???????????????????????????????????????????????????? T3
ROBINSON???????????????????????????????????????????????????? T4
ROBINSON???????????????????????????????????????????????????? HEX_TO_BIN

已選擇6行。

SQL> create index i_owner on test(owner);

索引已創建。

SQL> update test set owner='SYSMAN' where owner!='ROBINSON';

已更新50353行。

SQL> update test set owner='SYSTEM' where object_id>1000 and object_id<1020;

已更新19行。

SQL> commit;

提交完成。

SQL> update test set owner='SCOTT' where object_id>2000 and object_id<2005;

已更新4行。

SQL> select distinct owner from test;

OWNER
------------------------------------------------------------
ROBINSON
SYSTEM
SCOTT
SYS

SQL> BEGIN
? 2???? DBMS_STATS.GATHER_TABLE_STATS(ownname => 'ROBINSON',
? 3?????????????????????????????????? tabname => 'TEST',
? 4?????????????????????????????????? estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,
? 5?????????????????????????????????? method_opt => 'for all columns size repeat',
? 6?????????????????????????????????? degree => DBMS_STATS.AUTO_DEGREE,
? 7?????????????????????????????????? cascade=>TRUE
? 8?????????????????????????????????? );
? 9? END;
?10? /

PL/SQL 過程已成功完成。

SQL> set autot traceonly
SQL> select owner,object_name from test where owner not like 'SYS%';

已選擇10行。

執行計劃
----------------------------------------------------------
Plan hash value: 1357081020

--------------------------------------------------------------------------
| Id? | Operation???????? | Name | Rows? | Bytes | Cost (%CPU)| Time???? |
--------------------------------------------------------------------------
|?? 0 | SELECT STATEMENT? |????? | 25180 |?? 737K|?? 142?? (3)| 00:00:02 |
|*? 1 |? TABLE ACCESS FULL| TEST | 25180 |?? 737K|?? 142?? (3)| 00:00:02 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

?? 1 - filter("OWNER" NOT LIKE 'SYS%')

統計信息
----------------------------------------------------------
????????? 0? recursive calls
????????? 0? db block gets
????????? 0? consistent gets
????????? 0? physical reads
????????? 0? redo size
????????? 0? bytes sent via SQL*Net to client
????????? 0? bytes received via SQL*Net from client
????????? 0? SQL*Net roundtrips to/from client
????????? 0? sorts (memory)
????????? 0? sorts (disk)
???????? 10? rows processed

從此處可以看到選擇了10行，但是卻走了全表掃描，現在對其加HINT提示

SQL> select /*+ INDEX (test I_OWNER) */ owner,object_name from test where owner not like 'SYS%';

已選擇10行。

執行計劃
----------------------------------------------------------
Plan hash value: 469605390

---------------------------------------------------------------------------------------
| Id? | Operation?????????????????? | Name??? | Rows? | Bytes | Cost (%CPU)| Time???? |
---------------------------------------------------------------------------------------
|?? 0 | SELECT STATEMENT??????????? |???????? | 25180 |?? 737K|?? 490?? (1)| 00:00:06 |
|?? 1 |? TABLE ACCESS BY INDEX ROWID| TEST??? | 25180 |?? 737K|?? 490?? (1)| 00:00:06 |
|*? 2 |?? INDEX FULL SCAN?????????? | I_OWNER | 25180 |?????? |?? 140?? (3)| 00:00:02 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

?? 2 - filter("OWNER" NOT LIKE 'SYS%')

統計信息
----------------------------------------------------------
????????? 0? recursive calls
????????? 0? db block gets
????????? 0? consistent gets
????????? 0? physical reads
????????? 0? redo size
????????? 0? bytes sent via SQL*Net to client
????????? 0? bytes received via SQL*Net from client
????????? 0? SQL*Net roundtrips to/from client
????????? 0? sorts (memory)
????????? 0? sorts (disk)
???????? 10? rows processed

?

我們發現，強制加HINT提示所花的成本比全表掃描成本更高，這里要想優化這條SQL 必須改like

SQL> drop index i_owner;

索引已刪除。

SQL>? create? index f_owner on test(instr(owner,'SYS',1,1)) ;

索引已創建。

SQL> select? owner,object_name from test where instr(owner,'SYS',1,1)=0;

已選擇10行。

執行計劃
----------------------------------------------------------
Plan hash value: 535182827

---------------------------------------------------------------------------------------
| Id? | Operation?????????????????? | Name??? | Rows? | Bytes | Cost (%CPU)| Time???? |
---------------------------------------------------------------------------------------
|?? 0 | SELECT STATEMENT??????????? |???????? |?? 504 | 15120 |??? 52?? (0)| 00:00:01 |
|?? 1 |? TABLE ACCESS BY INDEX ROWID| TEST??? |?? 504 | 15120 |??? 52?? (0)| 00:00:01 |
|*? 2 |?? INDEX RANGE SCAN????????? | F_OWNER |?? 201 |?????? |??? 49?? (0)| 00:00:01 |
---------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

?? 2 - access(INSTR("OWNER",'SYS',1,1)=0)

統計信息
----------------------------------------------------------
????????? 0? recursive calls
????????? 0? db block gets
????????? 0? consistent gets
????????? 0? physical reads
????????? 0? redo size
????????? 0? bytes sent via SQL*Net to client
????????? 0? bytes received via SQL*Net from client
????????? 0? SQL*Net roundtrips to/from client
????????? 0? sorts (memory)
????????? 0? sorts (disk)
???????? 10? rows processed

當使用函數索引后，COST由原來的142下降到現在的52

總結：對于LIKE語句，我們可以使用instr函數來進行SQL調優

?

?

轉載于:https://www.cnblogs.com/hehe520/archive/2010/03/23/6330603.html

與50位技術專家面對面20年技術見證，附贈技術全景圖

總結

以上是生活随笔為你收集整理的SQL 语句中对于like 的调优的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。