From: Philip Hallstrom <postgresql@philip.pjkh.com>
To: Mark Fenbers <Mark.Fenbers@noaa.gov>
Cc: pgsql-sql@postgresql.org
Subject: Re: default value for select?
Date: Mon, 9 May 2005 10:18:04 -0700 (PDT)
Message-ID: <20050509101745.F26087@wolf.pjkh.com> (raw)
In-Reply-To: <427F9685.8050104@noaa.gov>
References: <427F9685.8050104@noaa.gov>
> I want to update a column in myTable. The value this column is set to depends on a
> nested select statement which sometimes returns 0 rows instead of 1. This is a
> problem since the column I'm trying to update is set to refuse nulls. Here's a
> sample:
>
> update myTable set myColumn = (Select altColumn from altTable where altColumn !=
> 'XXX' limit 1) where myColumn = 'XXX';
>
> MyColumn cannot accept nulls, but sometimes "Select altColumn ..." returns 0 rows,
> and thus, the query fails.
>
> Is there a way to set a default value to be inserted into myColumn if and when
> "select altColumn ..." returns zero rows?
COALESCE(value [, ...])
The COALESCE function returns the first of its arguments that is not null.
Null is returned only if all arguments are null. This is often useful to
substitute a default value for null values when data is retrieved for
display, for example:
SELECT COALESCE(description, short_description, '(none)') ...
Like a CASE expression, COALESCE will not evaluate arguments that are not
needed to determine the result; that is, arguments to the right of the
first non-null argument are not evaluated.
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To: pgsql-sql@postgresql.org
Cc: postgresql@philip.pjkh.com, Mark.Fenbers@noaa.gov
Subject: Re: default value for select?
In-Reply-To: <20050509101745.F26087@wolf.pjkh.com>
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