aha! sure. you weren't being vague. you just
needed to educate me.
some of us have used intersecting entities
through the years, but didn't know that there was
a fancy name for what we were doing. if my
memory weren't so bad, i'd use it to impress
people in the next interview.
in this case, simply do a three way multiple join
with the intersecting entity in the middle.
something like this:
select table1.col2, table 3.col2
from table1
left join table2 on table1.col1 = table2.col1
left join table3 on table2.col2 = table3.col1
or you could use an equal join with the
intersecting entity in the middle.
if you have a windows box that you can use as a
front end, i strongly recommend that you download
corereader because its point and click queries
can make a six way join look simple. then, it'll
show you the sql code. best of all is that it's
free. http://corereader.com
> Sorry for being vague. I think the closest thing I can find to it is,
> possibly, a three-way join. I'm trying to figure out how to write the
> query.
>
> I've got the following tables:
>
> systems
> ------------------------
> sys_name ID
> ------------------------
> Abrams 202
> Patriot 544
> Stinger 229
>
> ... and ...
>
> new_req
> ------------------------
> proj_name ID
> ------------------------
> Test Bed Alpha 344
> Tracked Wheels 989
> Battle Monitor 823
> Shoulder Harness 654
> Ammo Flask 454
> Spotter 773
>
> There may be multiple new requirements for a single system. To
> accommodate them, I created a new table -- an intersecting entity is
> what I recall it being called -- to bridge the two. I can't keep the
> multiple references to new_req in the systems table, nor can I keep them
> in the new_req table. As best I can figure, I need to have a bridge
> table ... e.g.,
>
> ie_sys_req
> ------------------------
> sys_id proj_name_id
> ------------------------
> 202 344
> 202 989
> 202 823
> 544 654
> 544 454
> 544 773
>
> If this seems peculiar, have patience with me I'm new at this. If it's
> right, let me know so I can breath a sigh of relief. And if the
> structure is right, could someone offer some guidance on how a query
> that allows me to query new_req using the intersecting entity (or
> three-way join, whatever it's called) would be written.
>
> Thanks,
>
>
> Rik Forgo
> JIST3
> Army Test, Training and Technology Integration Office (T3I)
> Diverse Technologies Corp.
> (c) 443.463.8571
> (h) 410.859.8474
>
>
> > -----Original Message-----
> > From: John Ragan [mailto:jragan@;arkansas.net]
> > Sent: Wednesday, November 06, 2002 6:55 PM
> > To: [EMAIL PROTECTED]; Richard Forgo
> > Subject: Re: Newbie: Intersecting entities
> >
> >
> > if a succinct statement is possible, perhaps you
> > could give us an idea of its nature?
> >
> > somebody may be familiar with the concept under a
> > different name.
> >
> >
> > > I'm trying to find some documentation on creating intersecting
> entities
> > > in MySQL, but haven't been able to track any info down on the MySQL
> site
> > > or on the web. At least we called them intersecting entities while
> I
> > > was in Oracle training (which was some time ago). I think I
> remember
> > > how to set them up, but I'd love to have something to refer to
> quickly
> > > before I start. Can anyone point me in the right direction?
> > >
> > >
> > > Rik Forgo
> > > JIST3
> > > Army Test, Training and Technology Integration Office (T3I)
> > > Diverse Technologies Corp.
> > > (c) 443.463.8571
> > > (h) 410.859.8474
> > >
> > >
> > >
> >
> >
> >
> > --
> > John Ragan
> > [EMAIL PROTECTED]
> > http://www.CoreReader.com/
> >
> >
> > ---------------------------------------------------------------------
> > Before posting, please check:
> > http://www.mysql.com/manual.php (the manual)
> > http://lists.mysql.com/ (the list archive)
> >
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>
>
>
--
John Ragan
[EMAIL PROTECTED]
http://www.CoreReader.com/
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