很多情况下我们都会需要复制源表数据以达到冗余数据的目的，那么到底是使用CREATE TABLE AS SELECT的CTAS方式，还是先建好表的结构然后再插入数据好呢？
我们来看看这2种方式的不同表现：
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE 10.2.0.4.0 Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 1
Next log sequence to archive 2
Current log sequence 2
/* 数据库处于归档模式下 */
SQL> select ss.name,ms.value from v$mystat ms,v$sysstat ss
2 where
3 ms.statistic#=ss.statistic#
4 and ss.name in ('undo change vector size','redo size');
NAME VALUE
---------------------------------------------------------------- ----------
redo size 0
undo change vector size 0
SQL> create table YOUYUS as select * from dba_objects;
Table created.
SQL> select ss.name,ms.value from v$mystat ms,v$sysstat ss
2 where
3 ms.statistic#=ss.statistic#
4 and ss.name in ('undo change vector size','redo size');
NAME VALUE
---------------------------------------------------------------- ----------
redo size 5783384
undo change vector size 15408
