From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Andrus" <kobruleht2(at)hot(dot)ee> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: FULL JOIN is only supported with merge-joinable join conditions |
Date: | 2007-05-20 01:42:24 |
Message-ID: | 20388.1179625344@sss.pgh.pa.us |
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Lists: | pgsql-general |
"Andrus" <kobruleht2(at)hot(dot)ee> writes:
> I try to port application to PostgreSQL 8.1+
> The following query runs OK in VFP but causes error in Postgres
> FULL JOIN is only supported with merge-joinable join conditions
> SELECT
> ...
> FROM iandmed
> FULL JOIN koosseis ON iandmed.ametikoht=koosseis.ametikoht
> AND iandmed.Kuluobj= koosseis.objekt1
> AND iandmed.AmetiKoht is not null
Uh, can't you just drop the "iandmed.AmetiKoht is not null" condition?
It seems redundant considering that "iandmed.ametikoht=koosseis.ametikoht"
isn't going to succeed when ametikoht is null.
In the long run we should teach hash join to support full-join behavior,
which would allow cases like this one to work; but it seems not very
high priority, since I've yet to see a real-world case where a
non-merge-joinable full-join condition was really needed. (FULL JOIN
being inherently symmetric, the join condition should usually be
symmetric as well...)
regards, tom lane
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