1、Rowid Format
2 、Locating a Row Using Rowid
Rowid is a data type that can be queried along with other columns in a table.
It has the following characteristics:
a、RowId is a unique identifier for each row in the database.
b、RowId is not stored explicitly as a column value.
c、Although the RowId does not directly give the physical address of a row,it can be used to licate the row.
d、Rowid provides the fastest means of acessing a row in a table.
e 、Rowids are stored in indexes to specify rows with a given set of key values.
Because a segment can only reside in one tablespace,by using the data object number,the oracle server can determine the tablespace that cantains a row.
the relative file number within the tablespace is used to lacate the file,
the block number is used to locate the block containing the row,
and the row number is used to locate the row directory entry for the row.
the row directory entry can be used to locate the begining of the row.
thus,Rowid can be used to locate any row within a database.
