We’ll discuss these in more detail in the Listing 4 When we add a unique clustered index to a view, we ‘materialize’ it.In other words, the ‘virtual table’ persists to disk, with its own page structure, and we can treat it just like a normal table.
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However, we can add a unique, clustered index to a view, creating an indexed view, and realize potential and sometimes significant performance benefits, especially when performing complex aggregations and other calculations.
In short, if an indexed view can satisfy a query, then under certain circumstances, this can drastically reduce the amount of work that SQL Server needs to do to return the required data, and so improve query performance.
To make it easier for our application to consume this data, we can create a view Listing 2 creates a view based on our query definition, as shown in Listing 2. In order to make one of these changes, we would have to drop the view, change the table, and then recreate the view (and any indexes on the view).
Now, each application simply has to run a much simpler query referencing the view, as shown in Listing 3.
Views are a valuable tool for the SQL Server Developer, because they hide complexity and allow for a readable style of SQL expression.
They aren't there for reasons of performance, and so indexed views are designed to remedy this shortcoming.
Figure 3 We see the exact same execution plan, output, and query cost if we run the query in Listing 1 again.
Although the use of the view made writing the query easier, it had no impact on query performance.
Any aggregations defined by the indexed view are now pre-computed, and any joins pre-joined, so the engine no longer has to do this work at execution time.