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 covid_json(info json);
insert into covid_json values('{"cases":[1983, 2188, 2615], "deaths": [78,84, 87]}'::json);
1 rows affected

select * from covid_json;

info

{"cases":[1983, 2188, 2615], "deaths": [78,84, 87]}

	select d.deaths, c.cases cases
	from covid_json cj
	cross join lateral json_array_elements(cj.info -> 'cases') with ordinality as d(deaths, rn)
	inner join lateral json_array_elements(cj.info -> 'deaths') with ordinality as c(cases, rn) on c.rn = d.rn

deaths
cases

1983
78

2188
84

2615
87