Virtual columns are new in Oracle 11g and allow a column to be dynamically filled with data based off an expression or function. Virtual columns do not store data on disk. Instead, the data is generated at run time. Virtual columns can be useful when there is an expression that is used on a table often. Instead of having to code the expression in the SELECT statement every time, the expression can be stored in a virtual column.
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In data warehouse environments, it is common to use materialized views to speed up the performance of commonly used queries. A materialized view is simply a pre-built query that stores the results of the query in a table. With the query rewrite capability enabled, Oracle can automatically make use of materialized views without the user even knowing.Let’s take a look at a simple order table for a generic store along with a denormalized table for dates in the order system and some sample data: