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).

  • 2
    Interesting question, I've come across these in some vendor databases, usually "settings" tables
    – Ben Brocka
    Dec 13, 2011 at 20:43

1 Answer 1


Singleton Table. In relational terms it is a relation with primary key ∅ (the empty set).

  • 12
    +1 A colleague suggested this moniker, too. (He also suggested "highlander table," which has a certain charm.)
    – pilcrow
    Dec 13, 2011 at 20:02
  • 3
    That's a singleton table, too.
    – miracle173
    Sep 2, 2014 at 16:47

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