Understanding Row Identifiers

Each row in an Oracle database has a unique row identifier, or rowid , which is used internally by the Oracle database to access the row. A rowid is an 18-digit number that is represented as a base-64 number, and it contains the physical address of a row in an Oracle database. You can view the rowid value for rows in a table by specifying the ROWID column in the select list of a query. The query in the following example retrieves the ROWID and customer_id columns from the customers table:

  SELECT ROWID, customer_id   FROM customers;  ROWID CUSTOMER_ID ------------------ ----------- AAAF4yAABAAAHeKAAA 1 AAAF4yAABAAAHeKAAB 2 AAAF4yAABAAAHeKAAC 3 AAAF4yAABAAAHeKAAD 4 AAAF4yAABAAAHeKAAE 5 

Notice the use of base-64 in this output. When you describe a table using the DESCRIBE command, ROWID doesn t appear in the output from the command because it is only used internally by the database. ROWID is known as a pseudo column.