一.物理读(physical read)
当数据块第一次读取到,就会缓存到buffer cache 中,而第二次读取和修改该数据块时就在内存buffer cache 了 以下是例子:
1.1 第一次读取:
C:"Documents and Settings"Paul Yi>sqlplus "/as sysdba"
SQL*Plus: Release 9.2.0.4.0 - Production on Thu Feb 28 09:32:04 2008
Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production
SQL> set autotrace traceonly
SQL> select * from test;
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT ptimizer=CHOOSE (Cost=2 Card=4 Bytes=8)
1 0 TABLE ACCESS (FULL) OF 'TEST' (Cost=2 Card=4 Bytes=8)
Statistics
----------------------------------------------------------
175 recursive calls
0 db block gets
24 consistent gets
9 physical reads --9个物理读
0 redo size
373 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
1 rows processed
1.2 第二次读取
SQL> select * from test;
Execution Plan
----------------------------------------------------------
0 &nbs
在Oracle8i或以上版本中，可以创建以下两种临时表：
1。会话特有的临时表
CREATE GLOBAL TEMPORARY <TABLE_NAME> (<column specification>)
ON COMMIT PRESERVE ROWS；
2。事务特有的临时表
CREATE GL ......
The RETURNING INTO clause allows us to return column values for rows affected by DML statements. The following test table is used to demonstrate this clause.
DROP TABLE t1;
DROP SEQUENCE t1_seq;
CREATE TABLE t1 (
id NUMBER(10),
description VARCHAR2(50),
CONSTRAINT t1_pk PRIMARY KEY (id)
......
说到软解析（soft prase）和硬解析（hard prase），就不能不说一下Oracle对sql的处理过程。当你发出一条sql语句交付Oracle，在执行和获取结果前，Oracle对此sql将进行几个步骤的处理过程：
1、语法检查（syntax check）
检查此sql的拼写是否语法。
2、语义检查（semantic check）
诸如检查sql语句中的访问对 ......
