Unique constraint : Unique « Constraints « SQL Server / T-SQL Tutorial






  1. SQL Server / T-SQL Tutorial
  2. Constraints
  3. Unique
2> CREATE TABLE customer_location
3> (
4> cust_id                 int    NOT NULL,
5> cust_location_number    int    NOT NULL,
6> CONSTRAINT customer_location_unique UNIQUE
7>     (cust_id, cust_location_number)
8> )
9> GO
1>
2> EXEC sp_helpconstraint customer_location
3> GO
Object Name



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customer_location




constraint_type                                                                                                                                    constraint_name
                                                                            delete_action update_action status_enabled status_for_replication constraint_keys











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UNIQUE (non-clustered)                                                                                                                             customer_location_unique
                                                                            (n/a)         (n/a)         (n/a)          (n/a)                  cust_id, cust_location_number












No foreign keys reference table 'customer_location', or you do not have permissions on referencing tables.
1>
2> drop table customer_location;
3> GO








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