IMMV with duplicate data in the pkey can't be created due to auto index creation

[aeg]

In pg_ivm 1.9, IMMV creation fails due to issues with index creation, which worked in 1.5.

expect

I want the ability to suppress auto index creation when needed to create IMMV.

how to reproduce

CREATE TABLE table_name ( id SERIAL PRIMARY KEY, json jsonb );

INSERT INTO table_name (json) VALUES ('{"a": [{"name":"b"},{"name": "c"},{"name": "d"}]}'::jsonb);
INSERT INTO table_name (json) VALUES ('{"a": [{"name":"e"},{"name": "f"},{"name": "g"}]}'::jsonb);

postgres=#  SELECT
    id,
    (element->>'name') AS name
FROM
    table_name,
    jsonb_array_elements(json->'a') AS element;
 id | name
----+------
  2 | b
  2 | c
  2 | d
  3 | e
  3 | f
  3 | g
(6 rows)

then create immv(failed)

postgres=# select create_immv('json_iv', $$SELECT
   id,
    (element->>'name') AS name
FROM
    table_name,
    jsonb_array_elements(json->'a') AS element$$);
ERROR:  could not create unique index "json_iv_index"
DETAIL:  Key (id)=(2) is duplicated.

Added DISTINCT in the SELECT then I could create the IMMV, but the execution plan is different, so it's inefficient and not what I need.

postgres=# select create_immv('json_iv', $$SELECT
   distinct id,
    (element->>'name') AS name
FROM
    table_name,
    jsonb_array_elements(json->'a') AS element$$);
NOTICE:  created index "json_iv_index" on immv "json_iv"
 create_immv
-------------
           6
(1 row)

postgres=# \d table_name
                            Table "public.table_name"
 Column |  Type   | Collation | Nullable |                Default
--------+---------+-----------+----------+----------------------------------------
 id     | integer |           | not null | nextval('table_name_id_seq'::regclass)
 json   | jsonb   |           |          |
Indexes:
    "table_name_pkey" PRIMARY KEY, btree (id)

[yugo-n]

Thank you for your reporting

Yes, this would be a bug of automatic index creation when the view has set-returning function in FROM clause. I'll fix this.

I want the ability to suppress auto index creation when needed to create IMMV.

Even though putting the bug-fix aside, your proposal also may make sense. This can be workaround for issues like this case and also it might be possible that users can find another efficient index.

[yugo-n]

I want the ability to suppress auto index creation when needed to create IMMV.

Or adding GUC parameter for this is better, instead of adding function arguments?