[prev in list] [next in list] [prev in thread] [next in thread] 

List:       pgsql-performance
Subject:    Re: [PERFORM] stats are way off on 8.4 b1
From:       Grzegorz_Jaśkiewicz <gryzman () gmail ! com>
Date:       2009-04-18 12:02:08
Message-ID: 2f4958ff0904180502x65dd00b5r614bba6ce73eb7ef () mail ! gmail ! com
[Download RAW message or body]

2009/4/18 Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>:
> Grzegorz Jaśkiewicz wrote:
>>
>> Can correlation be negative ?
>
> Yes, if the data in the column are in descending order. For example:
>
> postgres=# CREATE TABLE foo(id int4);
> CREATE TABLE
> postgres=# INSERT INTO foo SELECT 1000 - generate_series(1, 1000);
> INSERT 0 1000
> postgres=# ANALYZE foo;
> ANALYZE
> postgres=# SELECT attname, correlation FROM pg_stats  WHERE tablename='foo';
>  attname | correlation
> ---------+-------------
>  id      |          -1
> (1 row)

aye, thanks.


-- 
GJ

-- 
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance


[prev in list] [next in list] [prev in thread] [next in thread]