Multivariate statistics

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. +
+                      Ancient Roman grave inscription +