Using a CASE construct is good when you need non-string output but COALESCE is functionality equivalent and much less verbose when doing a default string output for null values.
From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general-owner@xxxxxxxxxxxxxx] On Behalf Of Brent Wood
Sent: Monday, April 25, 2011 6:33 PM
To: spluque@xxxxxxxxx; pgsql-general@xxxxxxxxxxxxxx
Subject: Re: concatenating with NULLs
Hi Seb,
Use CASE to change nulls to empty strings (or a placeholder) as below.
See: http://www.postgresql.org/docs/9.0/static/functions-conditional.html
if you want a placeholder in the result to indicate the presence of a null, try the second SQL:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
test=# select (case when 'a' isnull then '' else 'a' end) || (case when 'b' isnull then '' else 'b' end) || (case when NULL is null then '' end);
?column?
----------
ab
(1 row)
test=# select (case when 'a' isnull then '_' else 'a' end) || (case when 'b' isnull then '_' else 'b' end) || (case when NULL is null then '_' end);
?column?
----------
ab_
(1 row)
test=#
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
HTH,
Brent Wood
Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
>>> Seb <spluque@xxxxxxxxx> 04/26/11 10:21 AM >>>
Hi,
A query such as:
SELECT 'a' || 'b' || NULL;
returns a NULL. How can I ensure I get 'ab' in the result? I'm trying
to concatenate columns and one of them might have NULL values, which I
simply want to ignore.
Cheers,
--
Seb
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