Re: Optimizing Multiply Joins ??? - Mailing list pgsql-sql

From Meszaros Attila
Subject Re: Optimizing Multiply Joins ???
Date
Msg-id Pine.LNX.3.96.1000914151743.2542A-100000@draconis.csoma.elte.hu
Whole thread Raw
In response to Re: Optimizing Multiply Joins ???  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Optimizing Multiply Joins ???  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-sql
Hi,

> Actually, as the 7.1 code currently stands, a query that uses explicit
> JOIN operators like yours does will always be implemented in exactly
> the given join order, with no searching.  I haven't quite decided if
> that's a bug or a feature ...
Do you mean a "linear binary tree" like this is executed?
     /\    /\ f   /\ e  /\ d /\ ca  b
Or can we have some variations on the graph (with the samepreorder run: a,b,c,d,e,f) like this:
    /\               /  \              /   /\         /\  d /\        a /\  e  f         b  c            
We could give hints on the joins with brackets this way:((a,(b,c)),(d,(e,f)))
I'm not sure which version of standards allows to bracket joins,but I know sybase accepts the above form.
How difficult it looks to hack the parser to accept this form, and pass the meaning to the planner?

Attila




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