Re: TABLESAMPLE usage - Mailing list pgsql-general

From Tom Smith
Subject Re: TABLESAMPLE usage
Date
Msg-id CAKwSVFHLTJ1w0njMzNyh3nXmeax26_kgsyKFBtHRiU50QVV4eA@mail.gmail.com
Whole thread Raw
In response to Re: TABLESAMPLE usage  (Simon Riggs <simon@2ndQuadrant.com>)
List pgsql-general
Yeah. I am looking for fastest possible method that Postgresql would
use its internal data structure knowledge to walk through the timestamp index
and resturns every "nth" row

On Mon, Jan 25, 2016 at 5:56 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
On 25 January 2016 at 09:44, Matija Lesar <matija.lesar@gmail.com> wrote:
 
you can accomplish this with row_number():

WITH data_cte as (
    SELECT
        id,
        clock_timestamp() as ctimestamp
    FROM generate_series(1,1000) as id
    )
SELECT
    *
FROM
    (SELECT
        id,
        ctimestamp,
        row_number() OVER (ORDER BY ctimestamp) as rownum
    FROM data_cte

    ) as data_withrownumbers
WHERE
    rownum%100=1;

You can, but its not very fast.

--
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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