Date: Mon, 16 Jul 2018 20:04:34 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Yugo Nagata <nagata@sraoss.co.jp>
Cc: pgsql-hackers@postgresql.org, Teodor Sigaev <teodor@sigaev.ru>,
	Alexander Korotkov <aekorotkov@gmail.com>
Subject: Re: Fix error message when trying to alter statistics on included
 column
Message-ID: <20180717000433.ljup6n5mgxlgmeev@alvherre.pgsql>
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On 2018-Jun-28, Yugo Nagata wrote:

> According to the error message, it is not allowed to alter statistics on
> included column because this is "non-expression column".
> 
>  postgres=# create table test (i int, d int);
>  CREATE TABLE
>  postgres=# create index idx on test(i) include (d);
>  CREATE INDEX
>  postgres=# alter index idx alter column 2 set statistics 10;
>  ERROR:  cannot alter statistics on non-expression column "d" of index "idx"
>  HINT:  Alter statistics on table column instead.
> 
> However, I think this should be forbidded in that this is not a key column 
> but a included column. Even if we decide to support expressions in included
> columns in future, it is meaningless to do this because any statistics on 
> included column is never used by the planner.

I agree with this reasoning, so I pushed this patch.  Thanks!  I added a
couple of lines in the regress file for this feature also.

Teodor, Alexander, now would be the time to express dissent :-)

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services