临时表分为SESSION、TRANSACTION两种，SESSION级的临时表数据在整个SESSION都存在，直到结束此次SESSION；而TRANSACTION级的临时表数据在TRANACTION结束后消失，即COMMIT/ROLLBACK或结束SESSION都会清除TRANACTION临时表数据。

两种临时表的语法：

    create global temporary table 临时表名 on commit preserve|delete rows
    用preserve时就是SESSION级的临时表，用delete就是TRANSACTION级的临时表

1、session临时表

SQL> create global temporary table t_tmp_session
  2  (id varchar2(10),
  3  name varchar2(16))
  4  on commit preserve rows;

Table created

SQL> insert into t_tmp_session values('001','sqlee');

1 row inserted

SQL> commit;

Commit complete

SQL> select *from t_tmp_session;

ID         NAME
---------- ----------------
001        sqlee

commit后select发现数据还在，断开该session再select结果如下：

SQL> conn sys/sys as sysdba;
Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as SYS

SQL> conn sqlee/sqlee;
Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.1.0
Connected as sqlee

SQL> select *from t_tmp_session;

ID         NAME
---------- ----------------

现在发现临时表的数据已经不在了，这就是session级的临时表，session结束会清除数据。

2、TRANACTION临时表

SQL> create global temporary table t_tmp_tranaction
  2  (id varchar2(10),
  3  name varchar2(16))
  4  on commit delete rows;

Table created

SQL> insert into t_tmp_tranaction values('001','sqlee');

1 row inserted

SQL> select *from t_tmp_tranaction;

ID         NAME
---------- ----------------
001        sqlee

SQL> commit;

Commit complete

SQL> select *from t_tmp_tranaction;

ID         NAME
---------- ----------------

这就是tranaction级临时表，commit之后清除数据。

3、用as子句创建tranaction临时表

SQL> select * from t_tmp_session;

ID         NAME
---------- ----------------
001        sqlee

SQL> create global temporary table t_tmp_tranaction_as on commit delete rows
  2  as select *from t_tmp_session
  3  ;

Table created

SQL> select *from t_tmp_tranaction_as;

ID         NAME
---------- ----------------

因为create table.....as select ....是自动commit的，所以该表也没数据。