Date: Tue, 7 Aug 2018 13:44:55 -0400
From: Bruce Momjian <bruce@momjian.us>
To: madhav@cockroachlabs.com, pgsql-docs@lists.postgresql.org
Subject: Re: Multivariate statistics
Message-ID: <20180807174455.GE7297@momjian.us>
References: <153123827277.1406.2599036349134002521@wrigleys.postgresql.org>
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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  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
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