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Cross join-question: what to do when there's a null?

From: Rikard Bosnjakovic <rikard(dot)bosnjakovic(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Cross join-question: what to do when there's a null?
Date: 2010-08-06 15:26:23
Message-ID: AANLkTikukxG7avxG0R7CzhTSeAzC8X4SGK3HSGNaG7Uy@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-novice
Consider this small table:

ecdb=> SELECT id, name, package FROM components;
 id | name | package
----+------+---------
  1 |    1 |       2
  2 |    2 |
(2 rows)

The values in name and package refer to two other tables. I would like
to extract the name in the same query, so I run a cross-join:

ecdb=> SELECT c.id, x.name, c.package FROM components c,
component_names x WHERE c.id = x.id;
 id |  name  | package
----+--------+---------
  1 | BC547  |       2
  2 | 1N4148 |
(2 rows)


Next, I would also like the package name to be shown. However, since
there's a null (which is perfectly legal in this case) I am unable to
get it to work:

ecdb=> SELECT c.id, x.name, y.name FROM components c, component_names
x, packages y WHERE c.id = x.id AND c.package = y.id;
 id | name  | name
----+-------+------
  1 | BC547 | SO
(1 row)


The result I'm looking for is this:

 id |  name  | package
----+--------+---------
  1 | BC547  |       SO
  2 | 1N4148 |
(2 rows)

How do I run a cross join like this that will include the null element?


-- 
- Rikard

Responses

pgsql-novice by date

Next:From: Thom BrownDate: 2010-08-06 15:33:52
Subject: Re: Cross join-question: what to do when there's a null?
Previous:From: Joshua TolleyDate: 2010-08-06 13:57:22
Subject: Re: Best way to test/develop lots of nested functions?

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