--直接路径读方式 drop table test; create table test as select * from dba_objects where 1=2; set timing on insert /*+ append */ into test select * from t; commit; --注意这个直接路径方式插入试验输出的物理读（这是首次读哦） set autotrace traceonly select count(*) from test;
2.绑定变量使得速度加快
SQL>--未使用绑定变量 SQL> begin 2 for i in 1 .. 100000 3 loop 4 execute immediate 5 'insert into t values ( '||i||')'; 6 end loop; 7 commit; 8 end; 9 / PL/SQL 过程已成功完成。 已用时间: 00: 00: 43.50 SQL>--使用绑定变量 SQL> begin 2 for i in 1 .. 100000 3 loop 4 execute immediate 5 'insert into t values ( :x )' using i; 6 end loop; 7 commit; 8 end; 9 / PL/SQL 过程已成功完成。 已用时间: 00: 00: 04.77
3.批量提交使得速度加快
SQL> drop table t purge; 表已删除。 SQL> create table t(x int); 表已创建。 SQL> set timing on SQL> begin 2 for i in 1 .. 100000 loop 3 insert into t1 values (i); 4 commit; 5 end loop; 6 end; 7 / PL/SQL 过程已成功完成。 已用时间: 00: 00: 11.21 SQL> drop table t purge; 表已删除。 SQL> create table t(x int); 表已创建。 SQL> begin 2 for i in 1 .. 100000 loop 3 insert into t values (i); 4 end loop; 5 commit; 6 end; 7 / PL/SQL 过程已成功完成。 已用时间: 00: 00: 04.26
4.关闭日志提高性能
SQL> --测试直接路径读方式 SQL> drop table test; 表已删除。 SQL> create table test as select * from dba_objects where 1=2; 表已创建。 SQL> set timing on SQL> insert /*+ append */ into test select * from t; 已创建4664384行。 已用时间: 00: 00: 05.01 SQL> --测试nolgging关闭日志+直接路径读方式 SQL> drop table test; 表已删除。 SQL> create table test as select * from dba_objects where 1=2; 表已创建。 SQL> alter table test nologging; 表已更改。 SQL> set timing on SQL> insert /*+ append */ into test select * from t; 已创建4664384行。 已用时间: 00: 00: 04.39
5.避免对列进行运算，否则将用不到索引，除非使用函数索引。
drop table t purge;
create table t as select * from dba_objects;
create index idx_object_id on t(created);
set autotrace traceonly
set linesize 1000
--以下写法大量的出现在开发人员的代码中，是一个非常常见的通病,由于对列进行了运算，所以用不到索引，如下：
select * from t where trunc(created)>=TO_DATE('2013-12-14', 'YYYY-MM-DD')
and trunc(created)<=TO_DATE('2013-12-15', 'YYYY-MM-DD');
执行计划
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 12 | 2484 | 296 (2)| 00:00:04 |
|* 1 | TABLE ACCESS FULL| T | 12 | 2484 | 296 (2)| 00:00:04 |
--------------------------------------------------------------------------
1 - filter(TRUNC(INTERNAL_FUNCTION("CREATED"))>=TO_DATE(' 2013-12-14
00:00:00', 'syyyy-mm-dd hh24:mi:ss') AND
TRUNC(INTERNAL_FUNCTION("CREATED"))<=TO_DATE(' 2013-12-15 00:00:00',
'syyyy-mm-dd hh24:mi:ss'))
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
1049 consistent gets
0 physical reads
0 redo size
1390 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
---调整为如下等价语句后，就可以用到索引了。
select * from t where created>=TO_DATE('2013-12-14', 'YYYY-MM-DD')
and created<TO_DATE('2013-12-15', 'YYYY-MM-DD')+1;
执行计划
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 207 | 3 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 207 | 3 (0)| 00:00:01 |
|* 2 | INDEX RANGE SCAN | IDX_OBJECT_ID | 1 | | 2 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
2 - access("CREATED">=TO_DATE(' 2013-12-14 00:00:00', 'syyyy-mm-dd hh24:mi:ss')
AND "CREATED"<TO_DATE(' 2013-12-16 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
3 consistent gets
0 physical reads
0 redo size
1393 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
6.索引遇到like '%LJB' 或者是'%LJB%'的查询，是用不到索引的
create index idx_reverse_objname on t(reverse(object_name));
set autotrace on
select object_name,object_id from t where reverse(object_name) like reverse('%LJB');
OBJECT_NAME OBJECT_ID
---------------------------- --
AAALJB 8
执行计划
---------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 3596 | 509K| 290 (0)| 00:00:04 |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 3596 | 509K| 290 (0)| 00:00:04 |
|* 2 | INDEX RANGE SCAN | IDX_REVERSE_OBJNAME | 647 | | 6 (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
0 recursive calls
0 db block gets
5 consistent gets
0 physical reads
0 redo size
496 bytes sent via SQL*Net to client
415 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed