作者：劉穎博
時(shí)間：2004-6-12
mail：liuyingbo@126.com，請(qǐng)指正
轉(zhuǎn)載請(qǐng)注明出處及作者
本文討論的是關(guān)于oracle從8i開(kāi)始引進(jìn)object的概念后的rowid，即擴(kuò)展（extended）的rowid：
1.?????? rowid的介紹
先對(duì)rowid有個(gè)感官認(rèn)識(shí)：
SQL> select ROWID from Bruce_test where rownum<2;
ROWID
------------------ ----------
AAABnlAAFAAAAAPAAA
?
ROWID的格式如下：
數(shù)據(jù)對(duì)象編號(hào)??????? 文件編號(hào)??????? 塊編號(hào)?????????? 行編號(hào)
OOOOOO???????????? FFF??????????????? BBBBBB? RRR
我們可以看出，從上面的rowid可以得知：
AAABnl 是數(shù)據(jù)對(duì)象編號(hào)
AAF是相關(guān)文件編號(hào)
AAAAAP是塊編號(hào)
AAA 是行編號(hào)
怎么依據(jù)這些編號(hào)得到具體的十進(jìn)制的編碼值呢，這是經(jīng)常遇到的問(wèn)題。這里需要明白rowid的是基于64位編碼的18個(gè)字符顯示（數(shù)據(jù)對(duì)象編號(hào)(6) +文件編號(hào)(3) +塊編號(hào)(6)+?????? 行編號(hào)(3)=18位），其中
A-Z <==> 0 - 25 (26)
a-z <==> 26 - 51 (26)
0-9 <==> 52 - 61 (10)
+/ <==> 62 - 63 (2)
共64位，明白這個(gè)后，就可以計(jì)算出10進(jìn)制的編碼值，計(jì)算公式如下：
d * (b ^ p)
其中：b就是基數(shù)，這里就是64，p就是從右到左，已0開(kāi)始的位置數(shù)
比如：上面的例子
文件號(hào)AAF,具體的計(jì)算應(yīng)該是:
5*(64^0)=5；
0*(64^1)=0；
0*(64^2)=0；
文件號(hào)就是0+0+5=5
剛才提到的是rowid的顯示方式：基于64位編碼的18個(gè)字符顯示，其實(shí)rowid的存儲(chǔ)方式是：10 個(gè)字節(jié)即80位存儲(chǔ)，其中數(shù)據(jù)對(duì)象編號(hào)需要32 位，相關(guān)文件編號(hào)需要10 位，塊編號(hào)需要22，位行編號(hào)需要16 位，由此，我們可以得出：
32bit的object number，每個(gè)數(shù)據(jù)庫(kù)最多有4G個(gè)對(duì)象
10bit的file number，每個(gè)對(duì)象最多有1022個(gè)文件（2個(gè)文件預(yù)留）
22bit的block number，每個(gè)文件最多有4M個(gè)BLOCK
16bit的row number，每個(gè)BLOCK最多有64K個(gè)ROWS
2.?????? rowid相關(guān)的有用的sql
最簡(jiǎn)單的基于rowid的顯示方式得到的響應(yīng)的64位編碼對(duì)應(yīng)值的sql：
select rowid ,
substr(rowid,1,6) "OBJECT",
substr(rowid,7,3) "FILE",
substr(rowid,10,6) "BLOCK",
substr(rowid,16,3) "ROW"
from TableName;
OWID????????????? OBJECT?????? FILE?? BLOCK??????? ROW
------------------ ------------ ------ ------------ ------
AAABc4AADAAAGLUAAA AAABc4?????? AAD??? AAAGLU?????? AAA
AAABc4AADAAAGLUAAB AAABc4?????? AAD??? AAAGLU?????? AAB
AAABc4AADAAAGLUAAC AAABc4?????? AAD??? AAAGLU?????? AAC
AAABc4AADAAAGLUAAD AAABc4?????? AAD??? AAAGLU?????? AAD
AAABc4AADAAAGLUAAE AAABc4?????? AAD??? AAAGLU?????? AAE
通過(guò)dbms_rowid這個(gè)包，可以直接的得到具體的rowid包含的信息：
?
select dbms_rowid.rowid_object(rowid)? object_id, dbms_rowid.rowid_relative_fno(rowid) file_id,
dbms_rowid.rowid_block_number(rowid)? block_id ,dbms_rowid.rowid_row_number(rowid)? num from bruce_t where rownum<5;
OBJECT_ID??? FILE_ID?? BLOCK_ID??????? NUM
---------- ---------- ---------- ----------
????? 5944????????? 3????? 25300????????? 0
????? 5944????????? 3????? 25300????????? 1
????? 5944????????? 3????? 25300????????? 2
????? 5944????????? 3????? 25300????????? 3
一些使用ROWID的函數(shù)
ROWIDTOCHAR(rowid) ：將ROWID轉(zhuǎn)換成STRING
CHARTOROWID('rowid_string') ：將STRING轉(zhuǎn)換成ROWID
另外，就是自己寫(xiě)的一些函數(shù)：（下面的函數(shù)是網(wǎng)友eygle提供）
create or replace function get_rowid
(l_rowid in varchar2)
return varchar2
is
ls_my_rowid???? varchar2(200);?????????
rowid_type???? number;?????????
object_number???? number;?????????
relative_fno???? number;?????????
block_number???? number;?????????
row_number???? number;?
begin
?dbms_rowid.rowid_info(l_rowid,rowid_type,object_number,relative_fno, block_number, row_number);?????????
?ls_my_rowid := 'Object# is????? :'||to_char(object_number)||chr(10)||
??????? 'Relative_fno is :'||to_char(relative_fno)||chr(10)||
??????? 'Block number is :'||to_char(block_number)||chr(10)||
??????? 'Row number is?? :'||to_char(row_number);
?return ls_my_rowid ;
end;?????????
/
應(yīng)用上面的函數(shù)如下：
SQL> select get_rowid(rowid), name from bruce_t;
GET_ROWID(ROWID)???????????????????????????????????????????????????????????????? NAME
-------------------------------------------------------------------------------- --------------------------------
Object# is????? :5944????????????????????????????????????????????????????? BruceLau
Relative_fno is :3??????????????????????????????????????????????????????????????
Block number is :25300??????????????????????????????????????????????????????????
Row number is?? :0??????????????????????????????????????????????????????????????
Object# is????? :5944???????????????????????????????????????????????????? MabelTang
Relative_fno is :3??????????????????????????????????????????????????????????????
Block number is :25300??????????????????????????????????????????????????????????
Row number is?? :1???
?