Sorry, but I did not get you. I know that the filtering in the where clause and can be pushed up or down in the parsing tree depending on the optimizer. So in this certain case, the result could be computed first and filtered by the where clause later.
Regards
From: Tom Lane <tgl@sss.pgh.pa.us> To: salah jubeh <s_jubeh@yahoo.com> Cc: chris@chriscurvey.com; pgsql <pgsql-general@postgresql.org> Sent: Fri, April 15, 2011 5:49:35 PM Subject: Re: [GENERAL] correlated query as a column and where clause
salah jubeh <s_jubeh@yahoo.com> writes: > But, why I can not use the alias of the select statement ( as in the original > post) in the where clause.
The select list can only be computed after the where clause has filtered the rows, so such a thing would be circular.
