• I can create an index by means of a unique constraint:

    CREATE TABLE dbo.QotD

    (KeyColumn int NOT NULL PRIMARY KEY,

    RefColumn int NOT NULL,

    -- More column definitions

    CONSTRAINT FK_RefTab FOREIGN KEY (RefColumn)

    REFERENCES dbo.RefTab(RefTabKey),

    -- More constraints

    CONSTRAINT UQ_RefColumn UNIQUE(RefColumn)

    );

    Doesn't it count as answer #2? 🙂