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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
create table org_users (
id character varying (255),
settings_id character varying (255) -- fk: settings.id
);
create table settings (
id character varying (255), -- primary key settings_id
perdiem_settings character varying (255), -- jsonised fk to perdiems.id
floor_settings character varying (255) -- jsonised fk to floors.id
);
create table perdiems (
id integer, -- primary key
name character varying(255)
);
create table floors (
id integer, -- primary key
name character varying (255)
);
insert into perdiems (id, name) values (1, 'perdiem 1');
insert into perdiems (id, name) values (2, 'perdiem 2');
insert into perdiems (id, name) values (3, 'perdiem 3');
insert into floors (id, name) values (1, 'floor 1');
insert into floors (id, name) values (2, 'floor 2');
insert into floors (id, name) values (3, 'floor 3');
insert into settings (id, perdiem_settings, floor_settings) values ('setting1', '{"allowed_per_diem_ids":[1, 2]}', '{"allowed_floor_ids":[1]}');
insert into settings (id, perdiem_settings, floor_settings) values ('setting2', '{"allowed_per_diem_ids":[2, 3]}', '{"allowed_floor_ids":[1, 2]}');
insert into settings (id, perdiem_settings, floor_settings) values ('setting3', '{"allowed_per_diem_ids":[3, 1]}', '{"allowed_floor_ids":[1, 2, 3]}');
insert into org_users (id, settings_id) values ('user1', 'setting1');
insert into org_users (id, settings_id) values ('user2', 'setting2');
insert into org_users (id, settings_id) values ('user3', 'setting3');
insert into org_users (id, settings_id) values ('user4', null);
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select id , ARRAY[NULL] as perdiems ,ARRAY[NULL] as floors FROM org_users
WHERE settings_id IS NULL
UNION ALL
(
select ou.id, array_agg( DISTINCT pd.name ),
array_agg( DISTINCT f.name )
from org_users ou
join settings s on ( ou.settings_id = s.id )
cross join lateral
json_array_elements_text(((s.perdiem_settings)::json->'allowed_per_diem_ids')::json)
as jp(perdiem) join
perdiems pd
on pd.id = jp.perdiem::int OR jp.perdiem::int IS NULL
cross join lateral
json_array_elements_text(((s.floor_settings)::json->'allowed_floor_ids')::json)
as js(floor) join
floors f
on f.id = js.floor::int
GROUP BY ou.id
) ORDER BY id;
| id | perdiems | floors |
|---|---|---|
| user1 | {"perdiem 1","perdiem 2"} | {"floor 1"} |
| user2 | {"perdiem 2","perdiem 3"} | {"floor 1","floor 2"} |
| user3 | {"perdiem 1","perdiem 3"} | {"floor 1","floor 2","floor 3"} |
| user4 | {NULL} | {NULL} |