| From: | Tim Uckun <timuckun(at)gmail(dot)com> |
|---|---|
| To: | Peter Geoghegan <peter(dot)geoghegan86(at)gmail(dot)com> |
| Cc: | pgsql-general <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Selecting top N percent of records. |
| Date: | 2010-10-18 00:06:19 |
| Message-ID: | AANLkTimBXwCheGaet+qKdZ_xGJxOUe4zs6KMRMBYeEps@mail.gmail.com |
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| Thread: | |
| Lists: | pgsql-general |
> That is a bit problematic because it necessitates knowing the number
> of rows total, and slow counting is an idiosyncrasy of postgres.
>
> http://wiki.postgresql.org/wiki/Slow_Counting
>
> To get the top 10%:
>
> SELECT * FROM table LIMIT(SELECT (COUNT(*) * 0.1)::integer FROM table)
I think I wasn't making myself clear. I don't want the top 10% of the
rows. I want the rows with the top 10% of the values in a column.
In my case there is a very non linear set of values. The lowest value
is 1 and the vast majority of records have a 1 in the column. The
highest value might be in the tens of thousands. I want to pull up
the records that have the top ten percent values.
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