Re: correlated query as a column and where clause

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От salah jubeh
Тема Re: correlated query as a column and where clause
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Msg-id 734987.14706.qm@web161516.mail.bf1.yahoo.com
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Ответ на Re: correlated query as a column and where clause  (Tom Lane <tgl@sss.pgh.pa.us>)
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Hello Tom
 
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.

            regards, tom lane

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