Multiple unique keys
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In AL, a key definition now includes the Unique property that you can use to create a unique constraint on the table in SQL Server. A unique key ensures that records in a table do not have identical field values. With a unique key, when a table is validated, the key value is checked for uniqueness. If the table includes records with duplicate values, the validation fails. Another benefit of unique indexes is providing information to the query optimizer that helps produce more efficient execution plans.
Like primary keys, you can create unique secondary keys that are composed of multiple fields. In this case, it's the combination of the values in the secondary key that must be unique. For example, if you have a Customer table, you could create a unique key for the Name, Address, and City fields to make sure that there are no customers that have the same combination of values for these fields. Unlike primary keys, it is possible to define multiple unique secondary keys on a table.
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