PostgreSQL Essential Reference

OIDs

PostgreSQL makes use of object identifiers (OIDs) and temporary identifiers (TIDs) to correlate table rows with system tables and temporary index entries.

Every row inserted into a table in PostgreSQL has a unique OID associated with it. In fact, every table in PostgreSQL contains a hidden column named oid. For instance:

SELECT * FROM authors; 

Name              Title 
---------------------------------------------------
Bill Smith        Cooking for 6 Billion 
Sam Jones         Chicken Soup for the Publishers Soul 
SELECT oid, * FROM authors; 

Oid   Name              Title 
------------------------------------------------------------
17887 Bill Smith        Cooking for 6 Billion 
18758 Sam Jones         Chicken Soup for the Publishers Soul 

The key concept to understand with OIDs is that they are not ...