Subject: Multivariate statistics

From: PG Doc comments form <[email-masked]>
Date: Tue, 10 Jul 2018 15:57:52 +0000

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;)

---

From: Bruce Momjian <[email-masked]>
Date: Tue, 7 Aug 2018 13:44:55 -0400

> 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-masked]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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