Message-ID: <43D8F4FD.4040703@modgraph-usa.com>
Date: Thu, 26 Jan 2006 08:12:45 -0800
From: "Craig A. James" <cjames@modgraph-usa.com>
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To: pgsql-performance@postgresql.org
Subject: Re: Query optimization with X Y JOIN
References: <786c2f6d0601260206k2201a548p48af7c7fc085d3b2@mail.gmail.com>
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First, this isn't really the right place to ask -- this forum is about performance, not SQL syntax.

Second, this isn't a question anyone can answer in a reasonable length of time.  What you're asking for usually is taught in a class on relational database theory, which is typically a semester or two in college.

If you really need a crash course, dig around on the web for terms like "SQL Tutorial".

Good luck,
Craig


J@Planeti.Biz wrote:
> Hey guys, how u been. This is quite a newbie question, but I need to ask 
> it. I'm trying to wrap my mind around the syntax of join and why and 
> when to use it. I understand the concept of making a query go faster by 
> creating indexes, but it seems that when I want data from multiple 
> tables that link together the query goes slow. The slow is typically due 
> to expensive nested loops. The reason is, all my brain understands is:
>  
> select
>     tablea.data
>     tableb.data
>     tablec.data
> from
>     tablea
>     tableb
>     tablec
> where
>     tablea.pri_key = tableb.foreign_key AND
>     tableb.pri_key = tablec.foreign_key AND...
>  
>  From what I read, it seems you can use inner/outer right/left join on 
> (bla) but when I see syntax examples I see that sometimes tables are 
> omitted from the 'from' section of the query and other times, no. 
> Sometimes I see that the join commands are nested and others, no and 
> sometimes I see joins syntax that only applies to one table. From what I 
> understand join can be used to tell the database the fast way to murge 
> table data together to get results by specifiying the table that has the 
> primary keys and the table that has the foreign keys.
>  
> I've read all through the postgres docs on this command and I'm still 
> left lost. Can someone please explain to me in simple language how to 
> use these commands or provide me with a link. I need it to live right 
> now. Thanx.
>  
>