Re: Delete Duplicates with Using

FYI,

On 10/16/2017 8:58 AM, Igal @ Lucee.org wrote:
>
>>
>> test=*# with keep as (select max(ctid) as ctid from dubletten group
>> by c1,c2,c3) delete from dubletten where ctid not in (select ctid
>> from keep);
>>
>
> I like this solution, but would using a subquery be much slower than
> the implicit join of `using`?  My tables are not big in
> Postgres-standards, so it's probably not an issue, but I'm trying to
> learn as much as I can about Postgres now that I'm getting ready to
> move it to production.

I was able to compare the performance on a table with about 350k rows,
with duplicates over 7 columns and no indices.

The GROUP BY solution with the subquery (though I was using a simpler
version of it without a CTE), was taking over 30 seconds so I killed the
request.

I then ran the USING version which completed in 16 seconds and deleted
39 rows.

Best,

Igal Sapir
Lucee Core Developer
Lucee.org <http://lucee.org/>