Re: concatenating with NULLs

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(at)postgresql(dot)org
[mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of Brent Wood
Sent: Monday, April 25, 2011 6:33 PM
To: spluque(at)gmail(dot)com; pgsql-general(at)postgresql(dot)org
Subject: Re: [GENERAL] 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(at)gmail(dot)com> 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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