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Re: [HACKERS] Subselects are in CVS...

From: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
To: vadim(at)sable(dot)krasnoyarsk(dot)su (Vadim B(dot) Mikheev)
Cc: hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Subselects are in CVS...
Date: 1998-03-16 05:37:00
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Added to backend/optimizer/plan/README.

> This is some implementation notes and opened issues...
> First, implementation uses new type of parameters - PARAM_EXEC - to deal
> with correlation Vars. When query_planner() is called, it first tries to
> replace all upper queries Var referenced in current query with Param of 
> this type. Some global variables are used to keep mapping of Vars to 
> Params and Params to Vars. 
> After this, all current query' SubLinks are processed: for each SubLink 
> found in query' qual union_planner() (old planner() function) will be 
> called to plan corresponding subselect (union_planner() calls 
> query_planner() for "simple" query and supports UNIONs). After subselect 
> are planned, optimizer knows about is this correlated, un-correlated or 
> _undirect_ correlated (references some grand-parent Vars but no parent 
> ones: uncorrelated from the parent' point of view) query. 
> For uncorrelated and undirect correlated subqueries of EXPRession or 

Bruce Momjian                          |  830 Blythe Avenue
maillist(at)candle(dot)pha(dot)pa(dot)us              |  Drexel Hill, Pennsylvania 19026
  +  If your life is a hard drive,     |  (610) 353-9879(w)
  +  Christ can be your backup.        |  (610) 853-3000(h)

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