Hi Dani,
I understand that part :)
but what about the extra options you can specify in the join condition, like 'outer' , 'inner', 'full' etc
i dont see a circumstance when you would use the extra options...
----- Original Message -----
From: Dani Oderbolz <oderbolz@ecologic.de>
Date: Fri, 09 May 2003 10:29:51 +0200
To: pgsql-novice@postgresql.org
Subject: Re: [NOVICE] JOINS...
> Hi novice,
>
> >Whats the purpose of joins ?? is it the same as selecting from mulitple tables ?
> >
> >
> In a Relational Database liek Postgresql, you try the store data which
> as few redundancy as possible.
> The result is that you store the data in many tables - eg. persons and
> adresses will be separate
> (this process is called Normalisation).
> Now, to put the corresponding data together again, you need a join
> between the tables that belong together.
> In order to work, you need at least (numberOfTables -1) Join-Conditions,
> for exaple
>
> SELECT
> person.name,
> address.line1
> FROM
> person,
> address
> WHERE
> ' Here comes the Join Condition
> address.person_id = person.person_id
>
> If you do not specify the Join Condition, you will get all
> possible combinations of persons and addresses,
> the so called cartesian Product of the 2 tables.
>
> Cheers, Dani
>
>
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