Re: 3 tables join update

[rihad <rihad(at)mail(dot)ru>]

Richard Broersma Jr wrote:
> --- rihad <rihad(at)mail(dot)ru> wrote:
> > UPDATE Foo foo
> > SET foo.baz_id=baz.id
> > FROM Baz baz LEFT JOIN Bar bar ON (foo.bar_id=bar.id)
> > WHERE bar.id IS NULL;
>
> This query cannot work.  Basiclly, you are trying to set the foo.baz_id = baz.id for records in
> foo that do not yet exist.  Doing this is impossible.
Sorry the query failed victim of me trying to simplify it so I forgot 
the foo=bar join. Here's a 2 table join suffering from the same problem: 
I want the update only when bar.common_field IS NULL:

UPDATE Foo foo
SET ...
FROM LEFT JOIN Bar bar USING(common_field)
WHERE blah='blah' AND bar.common_field IS NULL;

ERROR:  syntax error at or near "JOIN"


I know I'm misusing UPDATE ... FROM because I don't really want Bar's 
values to go into Foo, but only using them for a conditional update 
(atomically I hope).