Oracle 11g增加列,并带默认值的新特性

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标题:Oracle 11g增加列,并带默认值的新特性

作者:惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

在11g以前,如果要在一个大表中增加一列,并设置默认值,那将是一个非常悲剧的事情.有些时候不得不选择在线重定义功能来实现该需求.而在11g中增加新列并设置默认值,只是简单的修改数据字典来实现该功能,大大提供效率
10g加列(默认值)

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE    10.2.0.1.0      Production
TNS for Linux: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production

SQL> create table t_xifenfei 
  2  as select object_id,object_name from dba_objects;

Table created.

SQL> select count(*) from t_xifenfei;

  COUNT(*)
----------
     49827

SQL> desc t_xifenfei
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 OBJECT_ID                                          NUMBER
 OBJECT_NAME                                        VARCHAR2(128)

SQL> set timing on                                                                      
SQL> alter table t_xifenfei add c_xff varchar2(100) default 'www.xifenfei.com' not null;

Table altered.

Elapsed: 00:00:06.13
--使用了6秒钟

SQL> select   rowid,
  2   dbms_rowid.rowid_relative_fno(rowid)rel_fno,
  3   dbms_rowid.rowid_block_number(rowid)blockno,
  4   dbms_rowid.rowid_row_number(rowid) rowno
  5  from t_xifenfei where object_name='OBJ$';

ROWID                 REL_FNO    BLOCKNO      ROWNO
------------------ ---------- ---------- ----------
AAAMwJAAEAAAAB8AAr          4        124         43

SQL> alter system dump datafile 4 block 124;

System altered.

Elapsed: 00:00:00.08

11g增加列(默认值)

SQL> select * from v$version;

BANNER
-----------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production

SQL> create table t_xifenfei 
  2  as select object_id,object_name from dba_objects;

Table created.

SQL> select count(*) from t_xifenfei;

  COUNT(*)
----------
     74605

SQL> select   rowid,
  2   dbms_rowid.rowid_relative_fno(rowid)rel_fno,
  3   dbms_rowid.rowid_block_number(rowid)blockno,
  4   dbms_rowid.rowid_row_number(rowid) rowno
  5  from t_xifenfei where object_name='OBJ$';

ROWID                 REL_FNO    BLOCKNO      ROWNO
------------------ ---------- ---------- ----------
AAASpRAAEAAAACrAAu          4        171         46

SQL> alter system dump datafile 4 block 171;

System altered.


SQL> set timing on
SQL> alter table t_xifenfei add c_xff varchar2(100) default 'www.xifenfei.com' not null;

Table altered.

Elapsed: 00:00:00.19
--只是使用了0.19秒

SQL> select   rowid,
  2   dbms_rowid.rowid_relative_fno(rowid)rel_fno,
  3   dbms_rowid.rowid_block_number(rowid)blockno,
  4   dbms_rowid.rowid_row_number(rowid) rowno
  5  from t_xifenfei where object_name='OBJ$';

ROWID                 REL_FNO    BLOCKNO      ROWNO
------------------ ---------- ---------- ----------
AAASpRAAEAAAACrAAu          4        171         46

Elapsed: 00:00:00.04
SQL> alter system dump datafile 4 block 171;

System altered.

通过10g和11g的增加相同列和默认值的对比可以发现,11g的速度要比10g快很多很多,下面我们通过上面dump出来相关的数据块来分析原因
dump分析
11g增加列之前dump

tab 0, row 0, @0x1f74
tl: 12 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 15
col  1: [ 5]  49 43 4f 4c 24
tab 0, row 1, @0x1f66
tl: 14 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 2f
col  1: [ 7]  49 5f 55 53 45 52 31
tab 0, row 2, @0x1f5b
tl: 11 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 1d
col  1: [ 4]  43 4f 4e 24

11g增加列之后dump

tab 0, row 0, @0x1f74
tl: 12 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 15
col  1: [ 5]  49 43 4f 4c 24
tab 0, row 1, @0x1f66
tl: 14 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 2f
col  1: [ 7]  49 5f 55 53 45 52 31
tab 0, row 2, @0x1f5b
tl: 11 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 1d
col  1: [ 4]  43 4f 4e 24
tab 0, row 3, @0x1f4f
tl: 12 fb: --H-FL-- lb: 0x0  cc: 2
col  0: [ 2]  c1 10
col  1: [ 5]  55 4e 44 4f 24

10g增加列之后dump
因为10g在没有增加列之前的dump和11g未增加列之前类似,所以未dump出来

tab 0, row 0, @0x1f63
tl: 29 fb: --H-FL-- lb: 0x2  cc: 3
col  0: [ 2]  c1 15
col  1: [ 5]  49 43 4f 4c 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 1, @0x1f44
tl: 31 fb: --H-FL-- lb: 0x2  cc: 3
col  0: [ 2]  c1 2d
col  1: [ 7]  49 5f 55 53 45 52 31
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 2, @0x1f28
tl: 28 fb: --H-FL-- lb: 0x2  cc: 3
col  0: [ 2]  c1 1d
col  1: [ 4]  43 4f 4e 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 3, @0x1f0b
tl: 29 fb: --H-FL-- lb: 0x2  cc: 3
col  0: [ 2]  c1 10
col  1: [ 5]  55 4e 44 4f 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d

对比发现11g在增加列之后,以前的数据dump出来的内容未有任何改变.也就是说:在10g中,我们增加一个列和默认值,会自动的增加到真实的数据中,而在11g中增加列和默认值并未真的加到11g的表中已经存在的数据中.
11g中插入新数据dump测试

SQL>  insert into chf.t_xifenfei(object_id,object_name)
  2  select object_id,object_name FROM DBA_OBJECTS;

74605 rows created.

SQL> commit;

Commit complete.

SQL> ALTER SYSTEM FLUSH BUFFER_CACHE;

System altered.

SQL> /

System altered.
--建议刷新

SQL> 
SQL> 
SQL> select   rowid,
  2   dbms_rowid.rowid_relative_fno(rowid)rel_fno,
  3   dbms_rowid.rowid_block_number(rowid)blockno,
  4   dbms_rowid.rowid_row_number(rowid) rowno
  5  from chf.t_xifenfei where object_name='OBJ$';

ROWID                 REL_FNO    BLOCKNO      ROWNO
------------------ ---------- ---------- ----------
AAASpRAAEAAAACrAAu          4        171         46
AAASpRAAEAAAB5TAAu          4       7763         46

SQL> ALTER SYSTEM DUMP DATAFILE 4 BLOCK 7763;

System altered.

--dump内容
tab 0, row 0, @0x4e3
tl: 29 fb: --H-FL-- lb: 0x1  cc: 3
col  0: [ 2]  c1 15
col  1: [ 5]  49 43 4f 4c 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 1, @0x500
tl: 31 fb: --H-FL-- lb: 0x1  cc: 3
col  0: [ 2]  c1 2f
col  1: [ 7]  49 5f 55 53 45 52 31
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 2, @0x51f
tl: 28 fb: --H-FL-- lb: 0x1  cc: 3
col  0: [ 2]  c1 1d
col  1: [ 4]  43 4f 4e 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
tab 0, row 3, @0x53b
tl: 29 fb: --H-FL-- lb: 0x1  cc: 3
col  0: [ 2]  c1 10
col  1: [ 5]  55 4e 44 4f 24
col  2: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d

通过这里看看出:在11g中后续插入的数据,默认值也插入到数据文件中

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Oracle 11g增加列,并带默认值的新特性》有 1 条评论

  1. 代海鹏 说:

    您好,请问 使用 在线重定义功能 该如何实现?您有相关博文吗, 对比PL/SQL 分批提交更新的方式,两种哪种有优势呢?

      [引用]  [回复]

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