Postgres 12

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.

select version();

version

PostgreSQL 12.0 (Debian 12.0-1.pgdg90+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516, 64-bit

create table t (a int);
insert into t (a) values (1) ;
1 rows affected

insert into t (a) values (2) ;
1 rows affected

insert into t (a) values (3) ;
1 rows affected

insert into t (a) values (5) ;
1 rows affected

select count(*) as c
from t
group by () ;

c

4