From: Arvind Balraman Subject: Re: Nested Select and Joins Date: 1998/03/03 Message-ID: <34FC9010.C8AD321D@ix.netcom.com>#1/1 Content-Transfer-Encoding: 7bit References: <34FCAFD1.9CD@bellsouth.net> Mime-Version: 1.0 To: ahairat@bellsouth.net Content-Type: text/plain; charset=us-ascii Organization: Netcom X-NETCOM-Date: Tue Mar 03 8:25:51 PM PST 1998 Newsgroups: comp.databases.oracle.tools Actually there are 5 types of select simple select ========= select * from emp nested select or sub select ================== select * from emp where deptno in (select * from dept where location='london'); the rdbms engine first evaluates the subquery first ie the dept query and then the outer query ie the emp query corelated sub-select ============= select a.* from emp a where a.deptno in (select b.deptno from dept b where a.dept_no = b.deptno) in this case the inner query refers a column from the outer query and the rdbms engine first evaluates the outer query ie the emp query and the inner query(ie the dept query) later. Ashish Kumar Hairat wrote: > Can somebody tell me what is nested select and its advantages? and also > what is the difference between outer join, inner join and equi join? > > Thanks -- Balaraman Arvind 151 Andrew Ave, Apt 215 Naugatuck, CT 06770 ph - (203)-723-1190(R) - (203)-459-7502(O) mail - dnivra@ix.netcom.com (R) abalaram@oxhp.com (O)