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Thread: How to delete the not DISTINCT ON entries

How to delete the not DISTINCT ON entries

From
Christoph Haller
Date:
Referring to the DISTINCT ON example

SELECT DISTINCT ON (location) location, time, report
FROM weatherReports
ORDER BY location, time DESC;

How would I delete those entries skipped by the DISTINCT ON expression?

TIA

Regards, Christoph

Re: How to delete the not DISTINCT ON entries

From
Achilleus Mantzios
Date:
O kyrios Christoph Haller egrapse stis Jun 16, 2004 :

> Referring to the DISTINCT ON example
> 
> SELECT DISTINCT ON (location) location, time, report
> FROM weatherReports
> ORDER BY location, time DESC;

maybe smth like 

delete from weatherReports where (location,time,report) not in 
(SELECT DISTINCT ON (location) location, time, report FROM weatherReports 
ORDER BY location, time DESC)

Note:
Order by is very important, since it affects which rows are deleted.

> 
> How would I delete those entries skipped by the DISTINCT ON expression?
> 
> TIA
> 
> Regards, Christoph
> 
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?
> 
>                http://archives.postgresql.org
> 

-- 
-Achilleus

Re: How to delete the not DISTINCT ON entries

From
Jean-Luc Lachance
Date:
If you do not have foreign key restrinctions, create a temp table from 
the select as:

CREATE TEMP TABLE tmp AS SELECT DISTINCT ON (location) location, time, 
report FROM weatherReports ORDER BY location, time DESC;

TRUNCATE weatherReports; INSERT INTO weatherReports SELECT * FROM tmp;

HTH


Achilleus Mantzios wrote:

> O kyrios Christoph Haller egrapse stis Jun 16, 2004 :
> 
> 
>>Referring to the DISTINCT ON example
>>
>>SELECT DISTINCT ON (location) location, time, report
>>FROM weatherReports
>>ORDER BY location, time DESC;
> 
> 
> maybe smth like 
> 
> delete from weatherReports where (location,time,report) not in 
> (SELECT DISTINCT ON (location) location, time, report FROM weatherReports 
> ORDER BY location, time DESC)
> 
> Note:
> Order by is very important, since it affects which rows are deleted.
> 
> 
>>How would I delete those entries skipped by the DISTINCT ON expression?
>>
>>TIA
>>
>>Regards, Christoph
>>
>>
>>
>>---------------------------(end of broadcast)---------------------------
>>TIP 6: Have you searched our list archives?
>>
>>               http://archives.postgresql.org
>>
> 
>