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2.1.1.4 Unique Constraints

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A unique constraint on a column enforces uniqueness of its data by creating an index (section 2.1.1.3) on that column and disallowing duplicate values in that column. Unique constraints use a sort order to determine the order in which the column data is indexed.

This protocol defines the Unique element (section 2.2.1.9) for specifying a unique constraint on a column in a table.