Hi Swathi,
Graphical based calculation views offer better performance compared to SQL based calculation views. But it will be difficult to implement complex business logic in graphical based calculation views. In such cases SQL based calculation views offer better flexibility. But you will have to compromise in performance side while using SQL based calculation views.In scenarios where graphical calculation views cannot implement business logic, It is always recommended to write SQL script and use CE functions which is more efficient than standard SQL. It is also adviced not to use both(CE function and Std SQL) together in a single calculation view.
have a look at the below discussion.
http://scn.sap.com/thread/3219325
Regards,
Nikhil Joy