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Materialized Views

In database terminology, a view is a named query that typically aggregates data from multiple tables. When using views, it is important to remember that querying a view will evaluate the query that defines the view. Repeated evaluation of the view – say from within a nested query – may seriously impact or even kill the performance of your application.

One solution to this performance problem is to use a “precomputed view”. Unlike an ordinary view, a precomputed view is stored in a table rather than computed on demand. When data in one of the aggregated tables changes, the update operation also updates the precomputed view table.

A great thing about precomputed views is that they can be implemented fully in SQL. Any code that accesses the database sees a precomputed view as a regular table. Also, if you have an existing regular view, you can change it into a precomputed view without having to modify any code that queries the view.

via Precomputed view: A cool and useful SQL pattern.

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