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UNIQUE Definition (unique_definition)Locate this document in the navigation structure


A UNIQUE definition ( unique_definition) in the CREATE TABLE statement defines the uniqueness of column value combinations.

  [CONSTRAINT <index_name>] UNIQUE (<column_name>,...)


SQL Tutorial, Indexes


Specifying a UNIQUE definition in a CREATE TABLE statement has the same effect as specifying the CREATE TABLE statement without a UNIQUE definition, but with a CREATE INDEX statement with UNIQUE.

  • Index name specified: The index generated is stored under this name in the database catalog.

  • No index name: The database system assigns a unique index name to the index.