Charges with Varible

gistfile1.txt

SET @total := (SELECT SUM(amount) FROM charges);

SELECT *, ROUND(amount / @total * 100) AS percent
FROM charges;

+----+--------+---------+
| id | amount | percent |
+----+--------+---------+
|  1 | 18.00  |      30 |
|  2 | 15.00  |      25 |
|  3 | 27.00  |      45 |
+----+--------+---------+