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Views Aren’t Tables

Grant Fritchey looks at how the query optimizer treats views:

The important point to note is that the optimizer is absolutely not treating the view like a table. The optimizer is treating the view like a query, which is all it is. This has both positive and negative impacts when it comes to query performance tuning and this view. You could spend all sorts of time “tuning” the view, only to find all that tuning you’ve done tossed out the window when the query doesn’t reference a column in the view and that causes the optimizer to rearrange the plan. I don’t want to convey that this is an issue. It’s not. I’m just trying to emphasize the point that a view is just a query.

In a subsequent post, Grant promises to talk about the potential perils of nested views.  That’s where people start running into trouble, when a nested view gets to be so complex that the query optimizer gives up and takes it literally.