SELECT * FROM テーブル名 ORDER BY 計算式;
計算した結果を並び替えます。
mysql> SELECT * FROM table_vote;
+------+------+-----+
| name | good | bad |
+------+------+-----+
| 佐藤     |    10 |    1 |
| 田中    |    30 | 29 |
| 鈴木     |    20 |    2 |
+------+------+-----+
mysql> SELECT * FROM table_vote ORDER BY good - bad;
+------+------+-----+
| name | good | bad |
+------+------+-----+
| 田中    |    30 | 29 |
| 佐藤     |    10 |    1 |
| 鈴木     |    20 |    2 |
+------+------+-----+