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wwh207 2004-07-19
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oracle数据库中美一条记录的唯一标识。
magicnbh 2004-07-16
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说的不错，不过那么多英文看得头都大了
smallcrocodile 2004-07-16
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数据库给每一列的唯一编号
yown 2004-07-14
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rowid是一个伪列,对应 块号,行号,行的序号..
wylwyl1130 2004-07-14
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rowidtochar()
xqg1130 2004-07-14
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學習,順便幫樓主頂一下
wolfAone 2004-07-14
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伪列：
伪列如同数据表的列，但它实际上不存储在表中
你可以从这些伪列中提取值
但你不能将值插入、更新或者删除它们
以下描述了这些伪列：
伪列如同数据表的列，但它实际上不存储在表中
你可以从这些伪列中提取值
但你不能将值插入、更新或者删除它们
以下描述了这些伪列：
wolfAone 2004-07-14
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Pseudocolumns
A pseudocolumn behaves like a table column, but is not actually
stored in the table. You can select from pseudocolumns, but you
cannot insert, update, or delete their values. This section
describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM
A pseudocolumn behaves like a table column, but is not actually
stored in the table. You can select from pseudocolumns, but you
cannot insert, update, or delete their values. This section
describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM
wolfAone 2004-07-14
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ROWID
For each row in the database, the ROWID pseudocolumn returns a row's
address. ROWID values contain information necessary to locate a
row:
* which data block in the data file
* which row in the data block (first row is 0)
* which data file (first file is 1)
In most cases, a ROWID value uniquely identifies a row in the
database. However, rows in different tables that are stored
together in the same cluster can have the same ROWID.
Values of the ROWID pseudocolumn have the datatype ROWID.
ROWID values have several important uses:
* They are the fastest means of accessing a single row.
* They can show you how a table's rows are stored.
* They are unique identifiers for rows in a table.
A ROWID does not change during the lifetime of its row. However,
you should not use ROWID as a table's primary key. If you delete
and reinsert a row with the Import and Export utilities, for
example, its ROWID may change. If you delete a row, Oracle may
reassign its ROWID to a new row inserted later.
Although you can use the ROWID pseudocolumn in the SELECT and WHERE
clauses of a query, these pseudocolumn values are not actually
stored in the database. You cannot insert, update, or delete a
value of the ROWID pseudocolumn.
EXAMPLE:
This statement selects the address of all rows that contain data for
employees in department 20:
SELECT ROWID, ename
FROM emp
WHERE deptno = 20
ROWID ENAME
----------------- ----------
0000000F.0000.0002 SMITH
0000000F.0003.0002 JONES
0000000F.0007.0002 SCOTT
0000000F.000A.0002 ADAMS
0000000F.000C.0002 FORD
For each row in the database, the ROWID pseudocolumn returns a row's
address. ROWID values contain information necessary to locate a
row:
* which data block in the data file
* which row in the data block (first row is 0)
* which data file (first file is 1)
In most cases, a ROWID value uniquely identifies a row in the
database. However, rows in different tables that are stored
together in the same cluster can have the same ROWID.
Values of the ROWID pseudocolumn have the datatype ROWID.
ROWID values have several important uses:
* They are the fastest means of accessing a single row.
* They can show you how a table's rows are stored.
* They are unique identifiers for rows in a table.
A ROWID does not change during the lifetime of its row. However,
you should not use ROWID as a table's primary key. If you delete
and reinsert a row with the Import and Export utilities, for
example, its ROWID may change. If you delete a row, Oracle may
reassign its ROWID to a new row inserted later.
Although you can use the ROWID pseudocolumn in the SELECT and WHERE
clauses of a query, these pseudocolumn values are not actually
stored in the database. You cannot insert, update, or delete a
value of the ROWID pseudocolumn.
EXAMPLE:
This statement selects the address of all rows that contain data for
employees in department 20:
SELECT ROWID, ename
FROM emp
WHERE deptno = 20
ROWID ENAME
----------------- ----------
0000000F.0000.0002 SMITH
0000000F.0003.0002 JONES
0000000F.0007.0002 SCOTT
0000000F.000A.0002 ADAMS
0000000F.000C.0002 FORD
ern 2004-07-13
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行的实际地址，包括了块信息等
dinya2003 2004-07-13
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rowid就象是邮递员送信时要找的信封上的家庭地址一样,每个rowid都不会重复,oracle查找通过它可以更快地查找到数据.
wylwyl1130 2004-07-12
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Internally, every database table has a ROWID pseudocolumn, which stores binary values called rowids. Each rowid represents the storage address of a row. A physical rowid identifies a row in an ordinary table. A logical rowid identifies a row in an index-organized table. The ROWID datatype can store only physical rowids. However, the UROWID (universal rowid) datatype can store physical, logical, or foreign (non-Oracle) rowids.
freddy2003 2004-07-12
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唯一标识一行记录
select rowid,* from 表名
试一下，你就明白了
select rowid,* from 表名
试一下，你就明白了
bzszp 2004-07-12
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每条记录的物理地址,
对数据库中记录行的作快检索方式就是使用rowid来进行查找。
对数据库中记录行的作快检索方式就是使用rowid来进行查找。
LGQDUCKY 2004-07-12
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rowid是数据库的一个伪列，建立表的时候数据库会自动为每个表建立ROWID列
用来唯一标识一行记录。
rowid是存储每条记录的实际物理地址，对记录的访问是基于ROWID。
用来唯一标识一行记录。
rowid是存储每条记录的实际物理地址，对记录的访问是基于ROWID。
