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

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SQL Server / T-SQL Tutorial » Constraints » Unique 
7. 10. 5. Unique constraint
2CREATE 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
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