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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 DISTINCT ON (id) *
FROM ( VALUES (1, 'y'),
(1, 'x'),
(2, 'z') ) s(id, type)
ORDER BY id,
CASE type
WHEN 'x' THEN 1
WHEN 'y' THEN 2
WHEN 'z' THEN 3
END;
| id | type |
|---|---|
| 1 | x |
| 2 | z |
SELECT 2