why inline view is different from other views?what is the use of naming it as a view

Question

As i know inline view is not a database object and it is just like writing a sub query in from clause so what is the use of naming it as a view .Simply we can call as a sub query.

Answer 1

It is Oracle naming convention. From Inline View and Subquery:

An inline view is a SELECT statement in the FROM-clause of another SELECT statement. In-line views are commonly used to simplify complex queries by removing join operations and condensing several separate queries into a single query.

This feature is commonly referred to in the MSSQL community as a derived table, and in the Postgres community simply refers to it as a subselect (subselects are inline views + subqueries in Oracle nomenclature).

A subquery (sub-query) is a SELECT statement in the WHERE- or HAVING-clause of another SELECT statement.

So when you used it with FROM it is called inline view:

SELECT * 
  FROM ( SELECT deptno, count(*) emp_count
         FROM emp
         GROUP BY deptno ) emp,
       dept
 WHERE dept.deptno = emp.deptno;

And when you used it with WHERE/HAVING it is called subquery:

SELECT ename, deptno 
  FROM emp 
 WHERE deptno = (SELECT deptno 
                   FROM emp 
                  WHERE ename = 'TAYLOR');