Adding a UNIQUE Constraint to an Existing Table : Unique « Constraints « SQL Server / T-SQL Tutorial

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SQL Server / T-SQL Tutorial » Constraints » Unique

7. 10. 1. Adding a UNIQUE Constraint to an Existing Table


The syntax is as follows:



ALTER TABLE table_name

ADD CONSTRAINT  constraint_name

UNIQUE  (column [ ASC | DESC ] [ ,...n ] )

7. 10. Unique
	7. 10. 1.	Adding a UNIQUE Constraint to an Existing Table
	7. 10. 2.	Unique constraints will also allow one NULL, whereas primary keys will not.
	7. 10. 3.	Unique Constraint: Enforce uniqueness on a column which is not the column used to primarily identify each row.
	7. 10. 4.	Unique constraints can be created when initially creating the table or added after.
	7. 10. 5.	Unique constraint
	7. 10. 6.	Creating a UNIQUE Constraints when creating a table
	7. 10. 7.	Creating UNIQUE Constraints on Existing Tables

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