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? 🙂