In datawarehouse slowly changing dimension with surrogate key are often used. It may happen, because of ETL poorly designed or other reasons, that ETL loads record not correctly versioned, violating the rule "for each unique value of the natural key there should be only one value of the surrogate key".
It would be nice to define a database constraint to enforce such an uniqueness , in Sql Server is not intuitive but is possible using a clustered unique index defined on an indexed view , defined as aggregate select.
In practice, the indexed view let us define an unique constraint based on aggregate select .
