Re: Specifying text to substitute for NULLs in selects

Thanks guys,

I'm aware of those options, what I was wondering was if there is a more generic way,
for example the Empress RDBMS allows 'set MSNULLVALUE "NA"', and all NULLs
will from then on be output as NA.

The COPY option is closest to a generic setting, but doesn't work with a select query,
just a table dump.

I guess something like the following will work from the shell, although it is hardly elegant :-)...

psql -d DB -Atc "select 'xxxx', attr, attr, attr, 'xxxx' from ....;" | sed 's/||/|NA|/' | sed 's/xxxx|//' | sed 's/|xxxx//' > data.txt

Slightly simpler than the case statement approach in Postgres is COALESCE()

eg: select COALESCE(attr,'NA') as attr from table;

but this still needs to be applied to every column in the outout which may have nulls. rather than a generic one off setting. A view using COALESCE() may be the easiest way for users to have this capability automatically..

Thanks,

Brent Wood

Brent Wood
DBA/GIS consultant
NIWA, Wellington
New Zealand
>>> Said Ramirez <sramirez(at)vonage(dot)com> 11/08/08 12:34 PM >>>
I think you are more after something like

SELECT CASE WHEN foo IS NULL THEN 'NA' END FROM bar.
-Said

Ivan Sergio Borgonovo wrote:
> On Thu, 6 Nov 2008 17:44:42 -0800 (PST)
> pcreso(at)pcreso(dot)com wrote:
>
> >
> > Hi,
> >
> > I can specify the text used to represent a null value in output
> > from copy, but I'd like to do something similar is select output,
> > eg: all NULL values are represented by NA or NaN.
> >
> > I can't find anything in the docs about this.
> >
> > This could be managed using case statements around all the columns
> > in the query, but is there a simpler way, like setting a system
> > variable to specify this?
>
> wtw_drupal=# create schema test;
> CREATE SCHEMA
> wtw_drupal=# create table test.test(c1 text);
> CREATE TABLE
> wtw_drupal=# insert into test.test values(null);
> INSERT 0 1
> wtw_drupal=# insert into test.test values('test');
> INSERT 0 1
> wtw_drupal=# \copy test.test to stdout null as 'BANANA'
> BANANA
> test
> wtw_drupal=# drop schema test cascade;
> NOTICE: drop cascades to table test.test
> DROP SCHEMA
>
> everything clearly explained in the COPY manual:
> http://www.postgresql.org/docs/8.1/static/sql-copy.html
>
> --
> Ivan Sergio Borgonovo
> http://www.webthatworks.it
>
>
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