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Re: Joining(?) question

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From	"David Kerber" <david.kerber@THRWHITE.remove-dii-this>
Subject	Re: Joining(?) question
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In article <72ed2328-62ae-491f-be9f-b6faad045e13
@q26g2000prq.googlegroups.com>, firstsql@ix.netcom.com says...
> On Nov 1, 5:17 pm, Lew <no...@lewscanon.com> wrote:
> > Lee Fesperman wrote:
> > > On Oct 30, 5:27 am, Lew <no...@lewscanon.com> wrote:
> > >> mdR wrote:
> > >>> SELECT BM.PARENT, BM.ITEM, IM.DESC
> > >>> FROM BM
> > >>> JOIN IM ON IM.ITEM = BM.ITEM
> > >>> WHERE BM.PARENT = 1;
> > >> Different RDBMSes vary wrt JOIN syntax.  But RGB's version should have worked,
> > >> too.
> >
> > >> Some allow
> >
> > >> SELECT BM.PARENT, BM.ITEM, IM.DESC
> > >>   FROM BM JOIN IM
> > >>   WHERE BM.PARENT = 1;
> >
> > >> if there's a FK on the ITEM column to the other table.
> >
> > > I realize that DBMS support of Standard SQL is weak, but which ones
> > > support those semantics? According to SQL92, an unqualified JOIN
> > > (without NATURAL, ON or USING) is the same as CROSS JOIN (that is, a
> > > Cartesian Product.)
> >
> > Oops, left out the word "NATURAL", as in "NATURAL JOIN".
> 
> That certainly makes a difference and will give the right results
> (given the table structure shown by the OP.) NATURAL joins on common
> column names between the two tables.
> 
> FK joining is non-standard and begs the question: Which FK for which
> table is used?

That syntax is only allowed if there is exactly one FK/PK combination 
that would satisfy the join.  Otherwise you get an error that says 
something to the effect of "there is more than one way to join table1 to 
table2"


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Re: Joining(?) question "David Kerber" <david.kerber@THRWHITE.remove-dii-this> - 2011-04-27 15:23 +0000

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