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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 T (UserId varchar(3), Orders int, Month int);
INSERT INTO T (UserId, Orders, Month)
VALUES ('XDT', 23, 1), ('XDT', 0, 4), ('FKR', 3, 6), ('GHR', 23, 4);
CREATE TABLE
INSERT 0 4
SELECT
SIGN(Orders),
ROUND(COUNT(*) * 1.000 / SUM(COUNT(*)) OVER (PARTITION BY Month)) AS Parts,
Month
FROM T
GROUP BY Month, SIGN(Orders)
ORDER BY Month, SIGN(Orders)
| sign | parts | month |
|---|---|---|
| 1 | 1 | 1 |
| 0 | 1 | 4 |
| 1 | 1 | 4 |
| 1 | 1 | 6 |
SELECT 4