Re: Fix error message when trying to alter statistics on included column

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org, Teodor Sigaev <teodor(at)sigaev(dot)ru>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Subject: Re: Fix error message when trying to alter statistics on included column
Date: 2018-07-17 00:04:34
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);
> postgres=# create index idx on test(i) include (d);
> 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
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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