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SQL Server

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by jabasd

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Difference Between Primary Key and Unique Constraints. y Primary key is using offen and y not Unique constraint.

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by tony hopkinson

Primary Keys are clustered Unique are not.

Primary keys can only be put on NOT NULL columns, you can build a Unique key on a nullable column, but bear in mind because it's unique, you can only have one null in the table at a time, so that particular facility is of limited value.

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