public inbox for [email protected]  

help / color / mirror / Atom feed

From: Bruce Momjian <[email protected]>
To: [email protected]
To: [email protected]
Subject: Re: Multivariate statistics
Date: Tue, 7 Aug 2018 13:44:55 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Tue, Jul 10, 2018 at 03:57:52PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/10/static/multivariate-statistics-examples.html
> Description:
> 
> Hi All, 
> 
> I'm a little confused by the documentation here: 
> https://www.postgresql.org/docs/10/static/multivariate-statistics-examples.html.
> 
> 
> In particular, the selectivity of the second query doesn't seem to match up
> with what is expected in the notes. I feel like I may be missing something?
> 
> 
> (I am referring to the output of this explain command: EXPLAIN (ANALYZE,
> TIMING OFF) SELECT * FROM t WHERE a = 1 AND b = 1;)

Uh, the first query shows an _estimate_ of rows=1, which does not match
the actual rows=100:

	Seq Scan on t  (cost=0.00..195.00 rows=1 width=8) (actual rows=100 loops=1)

The second query has it right:

	Seq Scan on t  (cost=0.00..195.00 rows=100 width=8) (actual rows=100 loops=1)

-- 
  Bruce Momjian  <[email protected]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

view thread (2+ messages)

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected]
  Subject: Re: Multivariate statistics
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox