标签归档：Identity Columns

在ORACLE 12C以前的版本中,如果要实现列自增长,需要通过序列+触发器实现,到了12C ORACLE 引进了Identity Columns新特性,从而实现了列自增长功能,和mysql,sql server类似功能.
使用语法

GENERATED ALWAYS AS IDENTITY方式测试

C:\Users\ffcheng>sqlplus chf/xifenfei@pdb

SQL*Plus: Release 12.1.0.2.0 Production on 星期二 3月 10 14:34:46 2015

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

上次成功登录时间: 星期五 12月 19 2014 21:00:26 +08:00

连接到:
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing opt
ions

XFF_PDB@CHF> select * from v$version;

BANNER                                                 CON_ID
-------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.          0
1.0.2.0 - 64bit Production

PL/SQL Release 12.1.0.2.0 - Production                      0
CORE    12.1.0.2.0      Production                          0
TNS for 64-bit Windows: Version 12.1.0.2.0 - Produ          0
ction

NLSRTL Version 12.1.0.2.0 - Production                      0

XFF_PDB@CHF>  create table t_xifenfei (id number GENERATED ALWAYS AS IDENTITY,na
me varchar2(100));

表已创建。

XFF_PDB@CHF> select object_name,object_type from user_objects;

OBJECT_NAME     OBJECT_TYPE
--------------- -----------------------
ISEQ$$_91982    SEQUENCE
T_XIFENFEI      TABLE

XFF_PDB@CHF> set long 10000
XFF_PDB@CHF> select dbms_metadata.get_ddl('TABLE','T_XIFENFEI') FROM DUAL;

DBMS_METADATA.GET_DDL('TABLE','T_XIFENFEI')
--------------------------------------------------------------------------------
  CREATE TABLE "CHF"."T_XIFENFEI"
   (    "ID" NUMBER GENERATED ALWAYS AS IDENTITY MINVALUE 1 MAXVALUE
   9999999999999999999999999999 INCREMENT BY 1 START WITH 1 
   CACHE 20 NOORDER  NOCYCLE  NOT NULL ENABLE,
        "NAME" VARCHAR2(100)
   ) SEGMENT CREATION DEFERRED
  PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255
 NOCOMPRESS LOGGING
  TABLESPACE "INMEMORY"

XFF_PDB@CHF> INSERT INTO T_XIFENFEI VALUES(1,'WWW.XIFNEFEI.COM');
INSERT INTO T_XIFENFEI VALUES(1,'WWW.XIFNEFEI.COM')
*
第 1 行出现错误:
ORA-32795: 无法插入到“始终生成”身份列


XFF_PDB@CHF> INSERT INTO T_XIFENFEI(name) VALUES('WWW.XIFNEFEI.COM');

已创建 1 行。

XFF_PDB@CHF> INSERT INTO T_XIFENFEI(name) VALUES('WWW.orasos.COM');

已创建 1 行。

XFF_PDB@CHF> commit;

提交完成。

XFF_PDB@CHF> col name for a30
XFF_PDB@CHF> select * from t_xifenfei;

        ID NAME
---------- ------------------------------
         1 WWW.XIFNEFEI.COM
         2 WWW.orasos.COM

XFF_PDB@CHF> update t_xifenfei set id=3 where id=2;
update t_xifenfei set id=3 where id=2
                      *
第 1 行出现错误:
ORA-32796: 无法更新“始终生成”身份列

XFF_PDB@CHF> delete from t_xifenfei where id=1;

已删除 1 行。

XFF_PDB@CHF> commit;

提交完成。

XFF_PDB@CHF> select ISEQ$$_91982.nextval from dual;

   NEXTVAL
----------
         3

XFF_PDB@CHF> INSERT INTO T_XIFENFEI(name) VALUES('WWW.ORASOS.COM');

已创建 1 行。

XFF_PDB@CHF> commit;

提交完成。

XFF_PDB@CHF> select * from t_xifenfei;

        ID NAME
---------- ------------------------------
         2 WWW.orasos.COM
         4 WWW.ORASOS.COM

XFF_PDB@CHF> ALTER SESSION SET EVENTS '10046 TRACE NAME CONTEXT FOREVER, LEVEL 1
2';

会话已更改。

XFF_PDB@CHF>  select value from v$diag_info where name='Default Trace File';

VALUE
--------------------------------------------------------------------------------

D:\APP\FFCHENG\diag\rdbms\xff\xff\trace\xff_ora_10628.trc

XFF_PDB@CHF> INSERT INTO T_XIFENFEI(name) VALUES('WWW.XIFENFEI.COM');

已创建 1 行。

XFF_PDB@CHF> COMMIT;

提交完成。

--跟踪trace文件
PARSING IN CURSOR #688719640 len=55 dep=0 uid=103 oct=2 lid=103 tim=15129490112 hv=961646460 
ad='7ff05d11a18' sqlid='21uzyjhwp33vw'
INSERT INTO T_XIFENFEI(name) VALUES('WWW.XIFENFEI.COM')
END OF STMT
PARSE #688719640:c=15600,e=18909,p=0,cr=44,cu=0,mis=1,r=0,dep=0,og=1,plh=2541165129,tim=15129490112
EXEC #688719640:c=0,e=347,p=0,cr=1,cu=5,mis=0,r=1,dep=0,og=1,plh=2541165129,tim=15129490731
STAT #688719640 id=1 cnt=0 pid=0 pos=1 obj=0 op='LOAD TABLE CONVENTIONAL  T_XIFENFEI (cr=1 pr=0 pw=0 time=296 us)'
STAT #688719640 id=2 cnt=1 pid=1 pos=1 obj=91983 op='SEQUENCE  ISEQ$$_91982 (cr=0 pr=0 pw=0 time=89 us)'
WAIT #688719640: nam='SQL*Net message to client' ela= 2 driver id=1413697536 #bytes=1 p3=0 obj#=-1 tim=15129490971

XFF_PDB@CHF> alter table t_xifenfei2 modify(id number GENERATED ALWAYS AS IDENTI
TY MINVALUE 1 MAXVALUE 99999999999999 INCREMENT BY 1 START WITH 1 CACHE  100);

表已更改。

XFF_PDB@CHF> drop sequence ISEQ$$_91982;
drop sequence ISEQ$$_91982
              *
第 1 行出现错误:
ORA-32794: 无法删除系统生成的序列

XFF_PDB@CHF> drop table t_xifenfei;

表已删除。

XFF_PDB@CHF> select object_name,object_type from user_objects where object_name=
'ISEQ$$_91982';

OBJECT_NAME          OBJECT_TYPE
-------------------- -----------------------
ISEQ$$_91982         SEQUENCE

XFF_PDB@CHF> select object_name,object_type from user_objects where object_name=
'ISEQ$$_91982';

OBJECT_NAME          OBJECT_TYPE
-------------------- -----------------------
ISEQ$$_91982         SEQUENCE

XFF_PDB@CHF> purge table t_xifenfei;

表已清除。

XFF_PDB@CHF> select object_name,object_type from user_objects where object_name=
'ISEQ$$_91982';

未选定行

这里的出来几个结论：
1. GENERATED ALWAYS AS IDENTITY 列无法人工指定值和修改该值
2. GENERATED IDENTITY 本质也是通过sequence实现
3. GENERATED IDENTITY 中sequence不能单独被删除
4. GENERATED IDENTITY 中的表删除,如果存在回收站中,该sequence依然存储,如果表被彻底删除,则sequence也被删除
5. GENERATED IDENTITY 中的sequence可以通过select 语句查询
6. 通过alert table 语句来修改GENERATED IDENTITY 的sequence相关值

GENERATED BY DEFAULT AS IDENTITY方式测试

XFF_PDB@CHF>  create table t_xifenfei2 (id number GENERATED BY DEFAULT AS IDENTI
TY,name varchar2(100)) tablespace users;

表已创建。

XFF_PDB@CHF> insert into t_xifenfei2 values (1,'www.xifenfei.com');

已创建 1 行。

XFF_PDB@CHF> insert into t_xifenfei2(name) values ('www.orasos.com');

已创建 1 行。

XFF_PDB@CHF> col name for a20
XFF_PDB@CHF> select * from t_xifenfei2;

        ID NAME
---------- --------------------
         1 www.xifenfei.com
         1 www.orasos.com

XFF_PDB@CHF> insert into t_xifenfei2 values (null,'www.xifenfei.com');
insert into t_xifenfei2 values (null,'www.xifenfei.com')
                                *
第 1 行出现错误:
ORA-01400: 无法将 NULL 插入 ("CHF"."T_XIFENFEI2"."ID")


XFF_PDB@CHF> desc t_xifenfei2
 名称                                      是否为空? 类型
 ----------------------------------------- -------- ---------------------------

 ID                                        NOT NULL NUMBER
 NAME                                               VARCHAR2(100)

得出结论：
1. GENERATED BY DEFAULT AS IDENTITY方式不能在该列中插入null值
2. GENERATED BY DEFAULT AS IDENTITY方式可以指定具体值插入

GENERATED BY DEFAULT ON NULL AS IDENTITY方式测试

XFF_PDB@CHF>  create table t_xifenfei3 (id number GENERATED BY DEFAULT on null A
S IDENTITY,name varchar2(100)) tablespace users;

表已创建。

XFF_PDB@CHF> desc t_xifenfei3
 名称                                      是否为空? 类型
 ----------------------------------------- -------- ----------------------------

 ID                                        NOT NULL NUMBER
 NAME                                               VARCHAR2(100)

XFF_PDB@CHF> insert into t_xifenfei3 values (null,'www.xifenfei.com');

已创建 1 行。

XFF_PDB@CHF> select * from t_xifenfei3;

        ID NAME
---------- --------------------
         1 www.xifenfei.com

测试结论：GENERATED BY DEFAULT ON NULL AS IDENTITY的列上可以查询null值，只是默认转换为对应的sequence值

传统自增长列实现方法

XFF_PDB@CHF> create table t_xifenfei4 (id number,name varchar2(100)) tablespace
users;

表已创建。

XFF_PDB@CHF> create sequence xff_sequence
  2  increment by 1
  3  minvalue 1
  4  nomaxvalue
  5  start with 1
  6  cache 20
  7  order;

序列已创建。

XFF_PDB@CHF> create or replace trigger xifenfei_id
  2  before insert on t_xifenfei4
  3  for each row
  4  begin
  5  select xff_sequence.nextval into :new.id from dual;
  6  end;
  7  /

触发器已创建

XFF_PDB@CHF> insert into t_xifenfei4(name) values('www.xifenfei.com');

已创建 1 行。

XFF_PDB@CHF> select * from t_xifenfei4;

        ID NAME
---------- --------------------
         1 www.xifenfei.com