Postgres 12

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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 mytable (id serial primary key);

CREATE TABLE

insert into mytable(id)
select generate_series(1,100000);

INSERT 0 100000

select * from mytable where id >= (
select random()*(max(id)-min(id))+min(id) from mytable)
order by id
limit 1;

id

21772

SELECT 1