Re: Statistical Analysis - Mailing list pgsql-general

From Steve Heaven
Subject Re: Statistical Analysis
Date
Msg-id 3.0.1.32.20000725084757.00b7bb30@mail.thornet.co.uk
Whole thread Raw
In response to Re: Statistical Analysis  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-general
At 20:18 24/07/00 -0400, you wrote:
>Sigh, forgot to mention the solution.  There's an undocumented function:
>
> * bool oidrand (oid o, int4 X)-
> *      takes in an oid and a int4 X, and will return 'true'
> *    about 1/X of the time.
>
>typically used like this:
>
>-- select roughly 1/10 of the tuples
>SELECT * FROM onek WHERE oidrand(onek.oid, 10);
>

It doesnt seem to work as you explain.
For a value of 1 you expect (nearly) all the tuples and two should return
half, but that not what I'm finding.

galore=> select count(*) from topten where room='HI';
count
-----
   14
(1 row)

galore=> SELECT * FROM topten WHERE room='HE' and oidrand(topten.oid, 1);
type|data                     |norder|room  |grp
----+-------------------------+------+------+---
B   |0764552503               |     1|HE    |
B   |0751327190               |     1|HE    |
B   |0718144392               |      |HE    |
B   |0500280754               |      |HE    |
B   |0028610091               |     1|HE    |
(5 rows)
galore=> SELECT * FROM topten WHERE room='HE' and oidrand(topten.oid, 2);
type|data                     |norder|room  |grp
----+-------------------------+------+------+---
B   |0764552503               |     1|HE    |
B   |0751327190               |     1|HE    |
B   |0718144392               |      |HE    |
(3 rows)
galore=> SELECT * FROM topten WHERE room='HE' and oidrand(topten.oid, 7);
type|data                     |norder|room  |grp
----+-------------------------+------+------+---
B   |0751327190               |     1|HE    |
B   |0718144392               |      |HE    |
(2 rows)
--
thorNET  - Internet Consultancy, Services & Training
Phone: 01454 854413
Fax:   01454 854412
http://www.thornet.co.uk

pgsql-general by date:

Previous
From: "Alex Bolenok"
Date:
Subject: Re: ROLLBACK automatically
Next
From: "anuj"
Date:
Subject: Describe structure.