relationid

Relationid, or relation identifier, is an internal, system-assigned unique identifier given to every relation in a relational database. A relation can be a base table, a view, an index, a sequence, or other database objects that are stored and referenced as relations. The primary purpose of a relationid is to provide a stable reference to the object independent of its human-facing name.

In practice, database engines store and use these identifiers in their system catalogs to track dependencies, permissions, storage details, and metadata. Because names may change over time, rely on the numeric id rather than the name when performing low-level operations, maintenance, or cross-reference tasks. The relationid helps the planner, executor, and catalog maintenance routines locate and manage the correct object.

A common example is seen in PostgreSQL, where each relation has an object identifier (OID) that serves as the relationid in internal catalogs such as pg_class. Queries can reveal it via system views, for instance by examining the oid column of pg_class for a given relname. It is important to note that the relationid is typically stable only for the life of the relation within a single database cluster; dropping and recreating the relation often yields a new identifier, and import/export operations may assign new IDs.

Across different database systems, the concept exists under similar names (for example, object_id), but the exact implementation, exposure, and persistence characteristics can vary. Users should treat relationids as internal references and rely on them primarily in catalogs, tooling, or internal APIs.