By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
CREATE TABLE `room` SELECT 1 id UNION SELECT 2;
CREATE TABLE `Room` SELECT 1 id UNION SELECT 3;
CREATE TABLE `RooM` SELECT 1 id UNION SELECT 2 UNION SELECT 3;
SELECT t1.id `Room Id`, t2.id `room Id`, t3.id `Room Id`
FROM `RooM` t1
LEFT JOIN `room` t2 USING (id)
LEFT JOIN `Room` t3 USING (id);
| Room Id | room Id | Room Id |
|---|---|---|
| 1 | 1 | 1 |
| 2 | 2 | null |
| 3 | null | 3 |