Since 8.1 PostgreSQL does not work this way anymore. The oid type is currently implemented as an unsigned four-byte integer. Therefore, it is not large enough

Since 8.1 PostgreSQL does not work this way anymore. The oid type is currently implemented as an unsigned four-byte integer. Therefore, it is not large enough to provide database-wide uniqueness in large databases, or even in large individual tables. So, using a user-created table's OID column as a primary key is discouraged. OIDs are best used only for references to system tables.[1] Besides, "object-relational" only means that it supports custom data types and inheritance, and at least custom data types are still a core feature of PostgreSQL. [1] https://www.postgresql.org/docs/8.1/datatype-oid.html https://www.postgresql.org/docs/8.1/datatype-oid.html