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Is there a specific term to describe a relation with a cardinality of one?
I'm thinking particularly of RDBMS "special" one-row tables, for example, DUAL (Oracle), SYSIBM.SYSDUMMY1 (DB2, Derby) and RDB$DATABASE (Interbase, Firebird).
Singleton Table. In relational terms it is a relation with primary key ∅ (the empty set).
Required, but never shown