Table Expressions in Microsoft SQL Server 2008 T-SQL
Table expressions can help you simplify your code, improve its maintainability, and encapsulate querying logic. When you need to use table expressions and are not planning to reuse their definitions, use derived tables or CTEs. CTEs have a couple of advantages over derived tables; you do not nest CTEs as you do derived tables, making CTEs more modular and easier to maintain. Also, you can refer to multiple instances of the same CTE, which you cannot do with derived tables.
When you need to define reusable table expressions, use views or inline TVFs. When you do not need to support input parameters, use views; otherwise, use inline TVFs.
Use the APPLY operator when you want to apply a table expression to each row from a source table, and unify all result sets into one result table.