Postgres 16

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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?.

select version();

version

PostgreSQL 16.0 (Debian 16.0-1.pgdg120+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit

SELECT 1

CREATE TABLE donors (
  city_name VARCHAR(50),
  blood_type VARCHAR(5));

INSERT INTO donors VALUES
  ('Amman','A+'),
  ('Amman','A-'),
  ('Amman','B+'),
  ('Amman','B-'),
  ('Irbid','A+'),
  ('Irbid','A-'),
  ('Irbid','B+');

CREATE TABLE

INSERT 0 7

SELECT * FROM donors WHERE city_name = amman;

ERROR:  column "amman" does not exist
LINE 1: SELECT * FROM donors WHERE city_name = amman;
                                               ^

SELECT * FROM donors WHERE city_name = 'amman';

city_name
blood_type

SELECT 0

SELECT * FROM donors WHERE city_name ILIKE 'amman'; 

city_name
blood_type

Amman
A+

Amman
A-

Amman
B+

Amman
B-

SELECT 4