Lists: | pgsql-sql |
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From: | Colin Fox <cfox(at)cfconsulting(dot)ca> |
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To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Left joins with multiple tables |
Date: | 2004-01-17 02:30:01 |
Message-ID: | pan.2004.01.17.02.29.56.311442@cfconsulting.ca |
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Lists: | pgsql-sql |
Hi, all.
I've got a bit of a problem here. I have 4 tables - people, a, b, c (not
the original names).
For each person in the people table, they may or may not have a record in
a, may or may not have a record in b, and may or may not have a record in
c.
Handling the first table (a) is easy:
select id, name
from people p left outer join a on a.person_id = p id;
But I'd like to be able to do something like:
select
id, name, a.field1, b.field2, c.field3
from
people p left outer join a on a.person_id = p id,
people p left outer join b on b.person_id = p.id,
people p left outer join c on c.person_id = p.id;
Naturally you can't repeat the 'people p' clause 3 times, but is there
some other syntax that would let me do this?
Thanks!
cf
From: | Richard Poole <richard(at)ruthie(dot)org> |
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To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: Left joins with multiple tables |
Date: | 2004-01-18 21:57:14 |
Message-ID: | 20040118215714.GA11708@guests.deus.net |
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Lists: | pgsql-sql |
On Sat, Jan 17, 2004 at 02:30:01AM +0000, Colin Fox wrote:
> For each person in the people table, they may or may not have a record in
> a, may or may not have a record in b, and may or may not have a record in
> c.
...
> But I'd like to be able to do something like:
>
> select
> id, name, a.field1, b.field2, c.field3
> from
> people p left outer join a on a.person_id = p id,
> people p left outer join b on b.person_id = p.id,
> people p left outer join c on c.person_id = p.id;
You can just chain the joins and the Right Thing will happen:
SELECT id, name, a.field1, b.field2, c.field3
FROM
people p
LEFT OUTER JOIN a ON (p.id = a.person_id)
LEFT OUTER JOIN a ON (p.id = b.person_id)
LEFT OUTER JOIN a ON (p.id = c.person_id)
I'm not sure that this behaviour is mandated by the SQL standard;
a certain other popular open source database-like product interprets
the same construction differently. But it does do what you want in
postgres.
Richard
From: | "Denis" <sqllist(at)coralindia(dot)com> |
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To: | <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: Left joins with multiple tables |
Date: | 2004-01-19 04:58:01 |
Message-ID: | 009b01c3de48$d379eae0$0f32a8c0@denisnew |
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Lists: | pgsql-sql |
Hi Colin,
Try
select id, name, a.field1, b.field2, c.field3
from
people p left outer join a on (a.person_id = p id)
left outer join b on (b.person_id = p.id)
left outer join c on (c.person_id = p.id);
HTH
Denis
----- Original Message -----
From: "Colin Fox" <cfox(at)cfconsulting(dot)ca>
To: <pgsql-sql(at)postgresql(dot)org>
Sent: Saturday, January 17, 2004 8:00 AM
Subject: [SQL] Left joins with multiple tables
> Hi, all.
>
> I've got a bit of a problem here. I have 4 tables - people, a, b, c (not
> the original names).
>
> For each person in the people table, they may or may not have a record in
> a, may or may not have a record in b, and may or may not have a record in
> c.
>
> Handling the first table (a) is easy:
>
> select id, name
> from people p left outer join a on a.person_id = p id;
>
> But I'd like to be able to do something like:
>
> select
> id, name, a.field1, b.field2, c.field3
> from
> people p left outer join a on a.person_id = p id,
> people p left outer join b on b.person_id = p.id,
> people p left outer join c on c.person_id = p.id;
>
> Naturally you can't repeat the 'people p' clause 3 times, but is there
> some other syntax that would let me do this?
>
> Thanks!
> cf
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster