Oracle的临时表

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 GLOBAL TEMPORARY <TABLE_NAME> (<column specification>)
    ON COMMIT DELETE ROWS；

ON COMMIT DELETE ROWS 说明临时表是事务指定，每次提交后ORACLE将截断表（删除全部行）
ON COMMIT PRESERVE ROWS 说明临时表是会话指定，当中断会话时ORACLE将截断表。

ON COMMIT DELETE ROWS 表名行只是在事务期间可见 

ON COMMIT PRESERVE ROWS 表名行在整个会话期间可见

建立临时表
   临时表的定义对所有会话SESSION都是可见的,但是表中的数据只对当前的会话或者事务有效.
   建立方法:
1) ON COMMIT DELETE ROWS 定义了建立事务级临时表的方法.
CREATE GLOBAL TEMPORARY TABLE admin_work_area
        (startdate DATE,
         enddate DATE,
         class CHAR(20))
      ON COMMIT DELETE ROWS;
例:
SQL> CREATE GLOBAL TEMPORARY TABLE admin_work_area
  2          (startdate DATE,
  3           enddate DATE,
  4           class CHAR(20))
  5        ON COMMIT DELETE ROWS;
SQL> create table permernate( a number);
SQL> insert into admin_work_area values(sysdate,sysdate,'temperary table');
SQL> insert into permernate values(1);
SQL> commit;
SQL> select * from admin_work_area;
SQL> select  * from permernate;
A
1
2)ON COMMIT PRESERVE ROWS 定义了创建会话级临时表的方法.
CREATE GLOBAL TEMPORARY TABLE admin_work_area
        (startdate DATE,
         enddate DATE,
         class CHAR(20))
     ON COMMIT PRESERVE ROWS;
例:
会话1:
SQL> drop table admin_work_area;
SQL> CREATE GLOBAL TEMPORARY TABLE admin_work_area
  2          (startdate DATE,
  3           enddate DATE,
  4           class CHAR(20))
  5       ON COMMIT PRESERVE ROWS;
SQL> insert into permernate values(2);
SQL> insert into admin_work_area values(sysdate,sysdate,'session temperary');
SQL> commit;
SQL> select * from permernate;
         A
----------
         1
         2
SQL> select * from admin_work_area;
STARTDATE  ENDDATE    CLASS
---------- ---------- --------------------
17-1?? -03 17-1?? -03 session temperary
会话2:
SQL> select * from permernate;
         A
----------
         1
         2
SQL> select * from admin_work_area;
未选择行.
会话2看不见会话1中临时表的数据.