Re: Extracting unique data from tables/views question

On Wed, Dec 29, 2010 at 7:52 AM, richard terry <rterry(at)pacific(dot)net(dot)au>wrote:

> This question will be a little vague I suspect as I don't know what I'm
> doing,
> but, there is some data below (actually is diabetic Hba1c data, I've copied
> from the fields in a view I've constructed):
>
> The view is:
>
> CREATE OR REPLACE VIEW research.diabetes_all_hba1c_results AS
> SELECT DISTINCT vwobservations.fk_patient,
> vwObservations.observation_date,
> vwobservations.value_numeric
> FROM documents.vwobservations where loinc = '4548-4'
> order by fk_patient, observation_date;
>
> and these are the fields and a little of the data:
>
> fk_patient:observation_date:hba1c
>
>
> 52;"2009-02-06";5.8
> 52;"2010-07-02";6.6
> 53;"2009-01-22";7.2
> 53;"2009-07-28";6.7
> 53;"2009-12-01";6.8
> 53;"2010-07-13";6.6
> 62;"2008-10-13";7.3
> 65;"2009-01-22";6.7
> 90;"2010-09-08";6.1
> 115;"2008-10-27";6.8
> 115;"2009-02-12";6.7
> 115;"2009-08-04";6.3
> 115;"2010-04-01";6.2
> 120;"2010-02-02";7.1
> 135;"2010-11-18";6.3
> 168;"2009-07-06";5.4
> 194;"2010-01-29";7.3
> 194;"2010-09-03";6.2
>
>
> You will note that there are mutliple measurements for each person, on
> particular dates, wheas what I want is only the latest value - ie the
> latest
> date.
>
> Any ideas/advice appreciated
>
>
You might want to use SELECT DISTINCT ON

http://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-DISTINCT

Try your query as:

CREATE OR REPLACE VIEW research.diabetes_all_hba1c_results AS
SELECT DISTINCT ON (vwobservations.fk_patient,
vwObservations.observation_date)
vwobservations.fk_patient, vwObservations.observation_date,
vwobservations.value_numeric
FROM documents.vwobservations where loinc = '4548-4'
order by fk_patient, observation_date;

HTH,
--
gurjeet.singh
@ EnterpriseDB - The Enterprise Postgres Company
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