From: Tony Wasson <ajwasson@gmail.com>
To: Mark Fenbers <Mark.Fenbers@noaa.gov>
Cc: pgsql-sql@postgresql.org
Subject: Re: default value for select?
Date: Mon, 9 May 2005 10:30:53 -0700
Message-ID: <6d8daee30505091030f5c7828@mail.gmail.com> (raw)
In-Reply-To: <427F9685.8050104@noaa.gov>
References: <427F9685.8050104@noaa.gov>
On 5/9/05, Mark Fenbers <Mark.Fenbers@noaa.gov> wrote:
> 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?
>
> Mark
Mark,
You can work around this by using a CASE statement. In this case, test
for a NULL from your subquery. This is not elegant at all, but it
should do what you are wanting.
update myTable set myColumn = (CASE
WHEN (Select altColumn from altTable where altColumn != 'XXX'
limit 1) IS NULL
THEN 'some default value'
ELSE (Select altColumn from altTable where altColumn != 'XXX' limit 1)
END)
where myColumn = 'XXX';
Hope this helps...
Tony
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To: pgsql-sql@postgresql.org
Cc: ajwasson@gmail.com, Mark.Fenbers@noaa.gov
Subject: Re: default value for select?
In-Reply-To: <6d8daee30505091030f5c7828@mail.gmail.com>
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