It is common for queries to restrict the result of a view so that only a few of the records are returned. When the view contains GROUP BY or UNION, it is preferable for the database server to only compute the result for the desired rows. Predicate push-down is performed for a predicate if, and only if, the predicate refers exclusively to the columns of a single view or derived table. A join predicate, for example, is not pushed down into the view.
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