Re: [GENERAL] Simulating an outer join

> Bruce Momjian wrote:
> >
> > I have been thinking about how to simulate an outer join. It seems the
> > best way is to do:
> >
> > SELECT tab1.col1, tab2.col3
> > FROM tab1, tab2
> > WHERE tab1.col1 = tab2.col2
> > UNION ALL
> > SELECT tab1.col1, NULL
> > FROM tab1
> > WHERE tab1.col1 NOT IN (SELECT tab2.col2 FROM tab2)
> >
> > Comments? I know someone was asking about this recently.
> >
>
> I wouldn't use IN ;-)
>
> SELECT table1.key, table2.value
> FROM table1, table2
> WHERE table1.key = table2.key
> UNION ALL
> SELECT table1.key, NULL
> FROM table1 WHERE NOT EXISTS
> (SELECT table2.key FROM table2 WHERE table1.key = table2.key);

Yes, this is our brain-damaged parser/optmizer that likes the usually
slower EXISTS with correlated subquery to the much clearer NOT IN.
Bummer.

I want to avoid having to put this workaround into my book, but I may
have no choice. The work around is so non-obvious as to be a terrible
hinderance for normal users.

--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
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