[postgis-users] Parcel household and dwelling unit data: add column if it doesn't exist

[Paul Ramsey]

RTFM on 'ALTER TABLE ADD COLUMN', 'CASE' and 'IS NULL'
P.

On Wed, Jun 29, 2011 at 10:33 AM, Conor Henley <conor at calthorpe.com> wrote:
> Hi all,
>
>
>
> I’m working with parcel data from several different regional sources.  In
> some cases, the parcel data comes with a households field, in others with a
> dwelling units field (in rare cases, both).  In all cases, I need both.
> Luckily, either can be calculated from the other using census multipliers.
>
>
>
> 1.       What is the best way to add the missing column when it does not
> exist?
>
>
>
> 2.       Then, how should I go about populating the newly created field
> using a calculation based on the other field (keeping in mind that I don’t
> want to overwrite either field in the case that both existed in the input
> data)?
>
>
>
> Ideally, I would be able to add the missing field in cases where it does not
> exist and populate its rows using a calculation based on the existing
> field.  Because this step must nest in a larger set of processes, it is
> impractical to check manually each time a new input goes through.  I’ve seen
> a good deal of discussion of this topic on forums but haven’t seen any clear
> solutions.
>
>
>
> Thanks,
>
>
>
>
>
> Conor Henley
>
> GIS/Regional Planning Intern
>
>
>
> C A L T H O R P E  A S S O C I A T E S
>
> 2095 ROSE STREET, SUITE 201, BERKELEY, CALIFORNIA, 94709 USA
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>
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>
>
>
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