While we retrieving data from either view or table? What will happend in the background? please explain
A view is just stored SQL, so in either case, we are just processing a SQL statement.
The way we process an SQL statement is a series of steps
- check that it is valid
- work out how best to run it
- read blocks from memory and/or disk for the objects concerned
- return results to the client
For a nicely detailed overview of this, check the Concepts manual here
http://docs.oracle.com/database/122/CNCPT/sql.htm#CNCPT216 (The entire Concepts manual is worth a read)