Re: Complex outer joins?

On Mon, 24 Mar 2003, Correia, Carla wrote:

>
> Hi,
>
> I've got PsotgreSQL 7.3.
>
> My problem is joins. I've seen the syntax on joins and have sucessefully
> used SQLs with joins, but I've got some other big SQL statements using many
> and complex
> joins.
> Simplified example:
>
> select G.SELID, G.TEXT,
> L.ID as SELLEVELID , L.SELLEVEL, L.LEVELJOIN, L.LEVELTEXT,
> C.ID as KRITERIENFELDID, C.SELFLD
> from G, L, C
> where
> and G.SELID = L.SELID (+)
> and L.SELID = C.SELID (+)
> and L.SELLEVEL = C.SELLEVEL (+)
>
> How can i write this in Postgres? As the problem is that I use one same
> table for varios joins. This is a problem in Postgres. Any ideas?
>
> When I use the same table in say 3 or 4 joins in one SQL, is the only
> solution unions?? Adn if so, the performance will certainly suffer?
>
I don't quite understand you question. but I presume that G, L,
and C are in fact the same table. I'm not sure what you mean by the (+)
more clarity is really required.
If however G, L, and C are the same table this query can be
rewritten as

select G.SELID, G.TEXT,
L.ID as SELLEVELID , L.SELLEVEL, L.LEVELJOIN, L.LEVELTEXT,
C.ID as KRITERIENFELDID, C.SELFLD
from table as G, table as L, table as C
where
and G.SELID = L.SELID
and L.SELID = C.SELID
and L.SELLEVEL = C.SELLEVEL;

Where table is the name of the table....
I hope that helps

Peter Childs