MySQL sort on a calculation

Question

Is it possible to sort on a calculation of 2 rows in mySQL? For example, I have 2 rows, lp and ap I'm trying to do something like this:

SELECT * from myTbl WHERE 1 ORDER BY (lp/ap)

Which isn't throwing an error, but its also not sorting by the results of that calculation. Is there a way to do this, or do I have to store lp/ap in the database?

Answer 1

 SELECT *, (lp/ap) AS calculation from myTbl ORDER BY calculation

This should do the trick, provided the (lp/ap) is valid.

Answer 2

you would probably have more chance doing

SELECT *, (lp/ap) as n from myTbl ORDER BY n

Answer 3

Yes, it is possible, and it does work. Check out the following 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); would return the same results.