Re: Eliminating unnecessary left joins - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Eliminating unnecessary left joins
Date
Msg-id 29136.1175902719@sss.pgh.pa.us
Whole thread Raw
In response to Eliminating unnecessary left joins  ("Ottó Havasvölgyi" <havasvolgyi.otto@gmail.com>)
Responses Re: Eliminating unnecessary left joins  (Andreas Pflug <pgadmin@pse-consulting.de>)
Re: Eliminating unnecessary left joins  ("Simon Riggs" <simon@2ndquadrant.com>)
List pgsql-hackers
"Ottó Havasvölgyi" <havasvolgyi.otto@gmail.com> writes:
> When using views built with left joins, and then querying against these
> views, there are a lot of join in the plan that are not necessary, because I
> don't select/use any column of each table in the views every time. Tables
> that are left joined and never referenced anywhere else in the query  should
> be removed from the plan.

That might cause you to get the wrong number of copies of some rows ---
what if a row of the left table should join to multiple rows on the right?
        regards, tom lane


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