Nested views--views that are called by another view--invariably start off with the best of intentions. Theoretically, there's nothing wrong with using a nested view as long as you're aware of the performance implications. Theoretically, the optimizer eliminates the intermediate abstraction of a nested view, ending up with the same query execution plan it would have devised if nested views hadn't been involved. But in practice, nested views create more problems than they solve.
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