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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 "order" (id serial primary key, customer_id int null);
CREATE TABLE
INSERT INTO "order" (customer_id) VALUES (NULL);
INSERT 0 1
SELECT id, COUNT(DISTINCT customer_id) FROM "order" GROUP BY "order"."id"
| id | count |
|---|---|
| 1 | 0 |
SELECT 1