Sub Queries Alias Name

SELECT * FROM (SELECT ROWNUM,ENAME,JOB,SAL FROM EMP WHERE ROWNUM<=8) E
WHERE E.ROWNUM BETWEEN 4 AND 7
In the above example is it compulsory to give the alias name for rownum? Why, When we can use FROM clause?

svp.kiran
Profile Answers by svp.kiran Questions by svp.kiran
Sep 28th, 2008
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sureshkumar.mtech
Profile Answers by sureshkumar.mtech Questions by sureshkumar.mtech

Oct 11th, 2008

Here compulsory to give the alias name for rownum because the column name is not exist in the table so it's show error for invalid columns specification.

The query should be below;
select * from (
select rownum as num, last_name, salary, id from employee
where rownum <= 4)x
where x.num between 2 and 3;