练习 DOUBLE INSERT
目标：从一张表取数据插入到另一张表中，此外需要为插入的目标表做一个应用级的日志表，也就是说在插入目标表的同时，还需要将相同的数据插入到日志表中。
在案例一中，我们给出了CREATE TRIGGER；OPEN CURSOR ;BULK INTO VARIABLE; DOUBLE INSERT; INSERT ALL 等方案。每个方案中也阐述了他的优缺点。
其中在DOUBLE INSERT，为了保证数据的一致性，又给出了四种思路，它们分别是锁，串行，临时表和as of 查询。下面将展现这四种思路SQL的展现。
当然DOUBLE INSERT 除了一致性的问题，还有原子性的问题，即有可有目标表和 日志表只成功了其它一个，或都没成功。关于原子性的问题。暂不讨论。
1.1思路一 锁
Drop table test;
Drop table T_ORG;
DROP TABLE T_LOG;
create table test as select * from all_objects ;
create table T_ORG as select * from all_objects WHERE 1=2;
create table T_LOG as select * from all_objects WHERE 1=2;
# --共享行专用(SRX)：阻止其他事务操作，其会会话不能对test表进行DML操作
SQL> lock table t in exclusive mode nowait;
Locked Object:
OWNEROS_USER_NAME OBJECT_NAME SIDSERIAL# LOCKED_MODE LOGON_TIM
------- ------------- ----------------- ---------- ----------- -------
SYS oracle TEST 18 17 6 26-APR-19
SYS@test>INSERT INTO T_ORG SELECT * FROM TEST;
72183 rows created.
SYS@test>INSERT INTO T_LOG SELECT * FROM TEST;
72183 rows created.
新开一个窗口执行delete 操作产生等待：
SYS@test2>delete from test where OBJECT_ID <10 ;
直到原来窗口事务结束。
SYS@test>COMMIT ;
问题：影响其它事务
1.2思路二 串行事务面临的问题 ora-01555
Drop table test;
Drop table T_ORG;
DROP TABLE T_LOG;
create table test as select * from all_objects ;
create table T_ORG as select * from all_objects WHERE 1=2;
create table T_LOG as select * from all_objects WHERE 1=2;
SYS@test>create undo tablespace undotbs datafile '/u01/app/oracle/oradata/test/undotbs.dbf' size 1M ;
Tablespace created.
SYS@test>alter system set undo_tablespace=undotbs;
SYS@test>show parameter undo ;
NAME TYPE VALUE
------------------------------------ ----------- ---------------------
undo_management string AUTO
undo_retention integer 900
undo_tablespace string UNDOTBS
declare
begin
INSERT INTO T_ORG SELECT * FROM TEST;
INSERT INTO T_LOG SELECT * FROM TEST;
Commit ;
end ;
/
*
ERROR at line 1:
ORA-30036: unable to extend segment by 8 in undo tablespace 'UNDOTBS'
ORA-06512: at line 3
SYS@test>select count(*) from T_ORG ;
COUNT(*)
----------
0
问题：UNDO 空间不足时，会报ORA-30036
如果UNDO空间被覆盖会报ORA-01555
1.3思路三 临时表
Drop table test;
Drop table T_ORG;
DROP TABLE T_LOG;
create table test as select * from all_objects ;
create table T_ORG as select * from all_objects WHERE 1=2;
create table T_LOG as select * from all_objects WHERE 1=2;
SYS@test>alter system set undo_tablespace=UNDOTBS1;
创建会话级别临时表：
SYS@test> create global temporary table temp1 on Commit Preserve Rows as select * from all_objects where 1=2 ;
把数据写入到临时表：
SYS@test>INSERT INTO temp1 SELECT * FROM all_objects;
72186 rows created.
SYS@test>INSERT INTO T_ORG SELECT * FROM temp1;
72186 rows created.
SYS@test>INSERT INTO T_LOG SELECT * FROM temp1;
72186 rows created.
问题：相关于写了三次，读了三次，对性能影响较大
1.4思路四 AS OF 查询
Drop table test;
Drop table T_ORG;
DROP TABLE T_LOG;
create table test as select * from all_objects ;
create table T_ORG as select * from all_objects WHERE 1=2;
create table T_LOG as select * from all_objects WHERE 1=2;
SYS@test>select current_scn from v$database ;
CURRENT_SCN
-----------
975216
SYS@test>INSERT INTO T_ORG SELECT * FROM test as of scn 975216;
72184 rows created.
SYS@test>INSERT INTO T_LOG SELECT * FROM test as of scn 975216;
72184 rows created.
前提是你要提前查询SCN 或时间，而且还是查询插入了2次。
针对以上的问题，最好的解决方案是利用ORACLE 的insert all
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