Inner Join Vs Database view Vs for all entries

Hi I know how to use and create inner join ( outer join) ,databse view and for all entries ....

I want to know since all of these three are used for the same purpose...which one is better....

and projection view ( why do we really create it ) ...is it faster ..because no correpsoding table or view is created in databe for the projection view ...then why do we really create it ...is it more optimized ???

Once database view is created then does the data in databse view is selected suring the select query ie at thr runtime or data is permanently stored in int in database....as far as i know .....data is selected at runtime in databse view..then why to create database view..instead I can use for all entries .........beacuse though using databse view we have one select query and using for all entries we have 2 select queries but internally when data is selected form a databse view.....database has to trigger two select queries....

In nutsheel i wan to understand the functionality ( efficcincy wise and how it works in background

) for all these three