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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 members as
select 1 as member_id, 'John ' as name, 2 as partner_id union all
select 2 as member_id, 'Eva ' as name, 1 as partner_id union all
select 3 as member_id, 'Peter ' as name, 4 as partner_id union all
select 4 as member_id, 'Mia ' as name, 3 as partner_id union all
select 5 as member_id, 'Rachel' as name, null as partner_id
5 rows affected
select m.*, mp.name as partner_name
from (select m.*
from members m
where m.member_id < m.partner_id or
m.partner_id is null
) m left join
members mp
on m.partner_id = mp.member_id
| member_id | name | partner_id | partner_name |
|---|---|---|---|
| 1 | John | 2 | Eva |
| 3 | Peter | 4 | Mia |
| 5 | Rachel | null | null |