Views can hide important information from the optimizer (especially
index information).
Really? AIUI, views-at least in PostgreSQL-are implemented using
PostgreSQL's rule system: the entire query is rewritten to include
the view query, and the optimizer sees the rewritten query. What the
optimizer sees is the same as if the view were inlined in the
original query.
That is a significant achievement, since many database systems do not
have that ability.
Another advantage of views is the ability to give zero rights to access
the objects the view is on, but allow the user to execute the view
itself. This allows limiting the view to not only a specific where
clause but also specific columns the user will be able to view.
Joshua D. Drake
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