Postgres 11

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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?.

drop table if exists survey_results;
create table survey_results(id serial primary key, name text, email text, payload json);
insert into survey_results (name, email, payload) values
(
    'Ying',
    'SmartStuff@gmail.com',
    '{"Product Name": "Calculator", "Product Price": "$54.99"}'),
(
    'Kendrick',
    'MrTexas@gmail.com',
    '{"Food Name": "Texas Toast", "Food Taste": "Delicious"}'),
(
    'Andy',
    'WhereTheBass@gmail.com',
    '{"Band Name": "MetalHeads", "Valid Member": "true"}')

DROP TABLE

CREATE TABLE

INSERT 0 3

select distinct json_object_keys(payload) as field_name
from survey_results

field_name

Band Name

Product Name

Food Taste

Valid Member

Product Price

Food Name

SELECT 6

select distinct payload->>'Food Name' as food_name
from survey_results
where payload->>'Food Name' is not null

food_name

Texas Toast

SELECT 1