Re: Query optimization with X Y JOIN

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



If I want my database to go faster, due to X then I would think that the issue is about performance. I wasn't aware of a paticular constraint on X.

I have more that a rudementary understanding of what's going on here, I was just hoping that someone could shed some light on the basic principal of this JOIN command and its syntax. Most people I ask, don't give me straight answers and what I have already read on the web is not very helpful thus far. ----- Original Message ----- From: "Craig A. James" <cjames@xxxxxxxxxxxxxxxx>
To: <pgsql-performance@xxxxxxxxxxxxxx>
Sent: Thursday, January 26, 2006 11:12 AM
Subject: Re: [PERFORM] Query optimization with X Y JOIN


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@xxxxxxxxxxx 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.


---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
      subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your
      message can get through to the mailing list cleanly




[Postgresql General]     [Postgresql PHP]     [PHP Users]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Books]     [PHP Databases]     [Yosemite]

  Powered by Linux