how to deteck empty tables in outer joins - Mailing list pgsql-novice

From Einar Karttunen
Subject how to deteck empty tables in outer joins
Date
Msg-id Pine.LNX.4.30.0102011347430.24468-100000@melkinpaasi.cs.Helsinki.FI
Whole thread Raw
In response to list of data types  ("Derek" <derek.mailer@virgin.net>)
Responses Re: how to deteck empty tables in outer joins
Re: how to deteck empty tables in outer joins
List pgsql-novice
Im trying to do an outerjoin of two tables. The second one might be
empty. Normally I would use a query like:

CREATE TABLE a ( id INTEGER );
CREATE TABLE b ( id INTEGER );

SELECT * FROM a,b
WHERE a.id=b.id
UNION ALL
SELECT * FROM a,b
WHERE a.id NOT IN (b.id)
;

If the seconf table is empty the result is null, because the cartesian
product of table and null is null. What I want is to include a condition
that if b has no rows then just add null for the value of b ie.
SELECT *,NULL FROM a; How can I implement this?

- Einar Karttunen




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