Sortowanie MySQL według obliczeń

Tak, jest to możliwe i działa. Sprawdź następujący test:

CREATE TABLE a(a INT, b INT);

INSERT INTO a VALUES (1, 1);
INSERT INTO a VALUES (1, 2);
INSERT INTO a VALUES (1, 3);
INSERT INTO a VALUES (1, 4);
INSERT INTO a VALUES (1, 5);
INSERT INTO a VALUES (1, 6);
INSERT INTO a VALUES (2, 1);
INSERT INTO a VALUES (2, 2);
INSERT INTO a VALUES (2, 3);
INSERT INTO a VALUES (2, 4);
INSERT INTO a VALUES (2, 5);
INSERT INTO a VALUES (2, 6);

SELECT a.a, a.b, (a/b) FROM a ORDER BY (a/b);

+------+------+--------+
| a    | b    | (a/b)  |
+------+------+--------+
|    1 |    6 | 0.1667 | 
|    1 |    5 | 0.2000 | 
|    1 |    4 | 0.2500 | 
|    2 |    6 | 0.3333 | 
|    1 |    3 | 0.3333 | 
|    2 |    5 | 0.4000 | 
|    1 |    2 | 0.5000 | 
|    2 |    4 | 0.5000 | 
|    2 |    3 | 0.6667 | 
|    2 |    2 | 1.0000 | 
|    1 |    1 | 1.0000 | 
|    2 |    1 | 2.0000 | 
+------+------+--------+

SELECT a.a, a.b FROM a ORDER BY (a/b); zwróci te same wyniki.