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?.

drop table if exists the_table cascade;
create table the_table (a text, b text, c text);
insert into the_table
values
('x','y','z'),
('p','q',null),
('s',null,'t'),
(null,'c', 'e'),
(null,'f', null),
(null,null, null);
6 rows affected

select a,b,c, (select count(*) from jsonb_object_keys(jsonb_strip_nulls(to_jsonb(t)))) as num_not_null
from the_table t;


a
b
c
num_not_null


x
y
z
3

p
q
null
2

s
null
t
2

null
c
e
2

null
f
null
1

null
null
null
0

a	b	c	num_not_null
x	y	z	3
p	q	null	2
s	null	t	2
null	c	e	2
null	f	null	1
null	null	null	0