Membership Count:5 PL/SQL Rowid 
Fixed-length binary. 
Pseudocolumn of a table. 
A DESCRIBE or SELECT * FROM MY_TABLE will not show the rowid; 
a SELECT rowid FROM MY_TABLE will show the hashed location. 
Fastest possible access to a given row 
Rowids do not change as long as the record exists. 
Rowids can not be changed during an insert or update transaction. 
Rowids can only be used to return a record. 
Rowids will change when EXPORTED or IMPORTED 
Extended Rowids use a base 64 encoding of the physical address for each row selected 
 

Rowid Structure

	BBBBBBBB.RRRR.FFFF

	BBBBBBBB=Block
	RRRR=Row within the Block
	FFFF=File Number

Extended Rowid Structure

   select rowid 
	,substr(rowid,1,6) "OBJECT"
	,substr(rowid,7,3) "FILE"
	,substr(rowid,10,6) "BLOCK"
	,substr(rowid,16,3) "ROW"
	from myTable;

INSTANCE_ID        OBJECT FIL BLOCK  ROW
------------------ ------ --- ------ ---
AAABUeAAQAAACsjAAg AAABUe AAQ AAACsj AAg

Oracle Functions to apply to a Rowid 

ROWIDTOCHAR(rowid)   converts a rowid into a string.

CHARTOROWID('rowid_string') converts a string into a rowid

Querying a record by rowid

	select rowidtochar(rowid) as id from my_table
	where rowid=chartorowid('AAABUeAAQAAACsjAAg')