Re: list of extended statistics on psql

Hi,

> The above query is so simple so that we would better to use the following query:
>
> # This query works on PG10 or later
> SELECT
>     es.stxnamespace::pg_catalog.regnamespace::text AS "Schema",
>     es.stxname AS "Name",
>     pg_catalog.format('%s FROM %s',
>         (SELECT pg_catalog.string_agg(pg_catalog.quote_ident(a.attname),', ')
>          FROM pg_catalog.unnest(es.stxkeys) s(attnum)
>          JOIN pg_catalog.pg_attribute a
>          ON (es.stxrelid = a.attrelid
>          AND a.attnum = s.attnum
>          AND NOT a.attisdropped)),
>     es.stxrelid::regclass) AS "Definition",
>     CASE WHEN 'd' = any(es.stxkind) THEN 'defined'
>     END AS "Ndistinct",
>     CASE WHEN 'f' = any(es.stxkind) THEN 'defined'
>     END AS "Dependencies",
>     CASE WHEN 'm' = any(es.stxkind) THEN 'defined'
>     END AS "MCV"
> FROM pg_catalog.pg_statistic_ext es
> ORDER BY 1, 2;
>
>  Schema |    Name    |    Definition    | Ndistinct | Dependencies | Dependencies
> --------+------------+------------------+-----------+--------------+--------------
>  public | hoge1_ext  | a, b FROM hoge1  | defined   | defined      | defined
>  public | hoge_t_ext | a, b FROM hoge_t | defined   | defined      | defined
> (2 rows)
>
>
> I'm going to create the WIP patch to use the above query.
> Any comments welcome. :-D

Attached patch is WIP patch.

The changes are:
- Use pg_statistic_ext only
- Remove these statuses: "required" and "built"
- Add new status: "defined"
- Remove the size columns
- Fix document

I'll create and send the regression test on the next patch if there is
no objection. Is it Okay?

Regards,
Tatsuro Yamada