From: Sheryl Canter
Date: February 26 2003 3:56pm
Subject: Re: Help needed with SQL...
List-Archive: http://lists.mysql.com/mysql/133422
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I've never seen opening a table twice and then doing a join back with
itself. Am I wording this correctly? Is that how to describe what you're
doing?

Thanks for posting this to the full list.

    - Sheryl


----- Original Message -----
From: "Don Read" <dread@stripped>
To: <Jun.Han@stripped>
Cc: <mysql@stripped>; <autumn@stripped>
Sent: Wednesday, February 26, 2003 5:11 AM
Subject: RE: Help needed with SQL...



On 26-Feb-2003 Jun.Han@stripped wrote:
> Yes , I had use this query statement in my MySQL server,
> But I have a query about it.
> Why are you use "WHERE a.groupname=b.groupname AND members.id=b.memberid
> AND a.memberid=1"?
> Can you give me a explain or give me a advise!
>

Sure.

mysql> SELECT DISTINCT members.* FROM members, groups as a, groups as b
    -> WHERE a.groupname=b.groupname AND members.id=b.memberid
    -> AND a.memberid=1;


The 'a.memberid=1' clause looks up the groups that member 1 belongs to in
the
groups table (as a), giving 'group1' & 'group2'.

Then it joins back against the groups table (as b) with the
'a.groupname=b.groupname' clause to get the folks that belong to these
group(s).

Finally the 'members.id=b.memberid' bit selects the records out of the
members
table, with the DISTINCT function suppressing any duplicates.

Clear as mud?

(I could've be a little more obvious if I'd put the 'a.memberid=1' clause
first. Sorry ...)

Regards,
--
Don Read                                       dread@stripped
-- It's always darkest before the dawn. So if you are going to
   steal the neighbor's newspaper, that's the time to do it.
                            (53kr33t w0rdz: sql table query)

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