akumulasi reset tiap bulan

DROP TABLE IF EXISTS transactions;
CREATE TABLE transactions(
    id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    tgl DATE,
    amount INT null
) ENGINE=MyISAM;

INSERT INTO transactions VALUES
(1,'2020-05-30',5200),
(2,'2020-05-31',1500),
(3,'2020-06-01',3200),
(4,'2020-06-02',3500),
(5,'2020-06-03',1200),
(6,'2020-06-04',5200),
(7,'2020-06-05',7300),
(8,'2020-06-06',3400),
(9,'2020-06-07',4900),
(10,'2020-06-08',8600),
(11,'2020-06-09',1700),
(12,'2020-06-10',5500);

 select * from transactions;
+----+------------+--------+
| id | tgl        | amount |
+----+------------+--------+
|  1 | 2020-05-30 |   5200 |
|  2 | 2020-05-31 |   1500 |
|  3 | 2020-06-01 |   3200 |
|  4 | 2020-06-02 |   3500 |
|  5 | 2020-06-03 |   1200 |
|  6 | 2020-06-04 |   5200 |
|  7 | 2020-06-05 |   7300 |
|  8 | 2020-06-06 |   3400 |
|  9 | 2020-06-07 |   4900 |
| 10 | 2020-06-08 |   8600 |
| 11 | 2020-06-09 |   1700 |
| 12 | 2020-06-10 |   5500 |
+----+------------+--------+


SELECT x.tgl
     , x.amount
     , SUM(y.amount) AS accu
FROM
     (
       SELECT *
       FROM transactions
     ) x
  JOIN
     (
       SELECT *
       FROM transactions
     ) y
    ON (y.tgl <= x.tgl AND DATE_FORMAT(y.tgl,'%Y%m')=DATE_FORMAT(x.tgl,'%Y%m'))
 GROUP
    BY x.tgl,x.amount;

+------------+--------+-------+
| tgl        | amount | accu  |
+------------+--------+-------+
| 2020-05-30 |   5200 |  5200 |
| 2020-05-31 |   1500 |  6700 |
| 2020-06-01 |   3200 |  3200 |
| 2020-06-02 |   3500 |  6700 |
| 2020-06-03 |   1200 |  7900 |
| 2020-06-04 |   5200 | 13100 |
| 2020-06-05 |   7300 | 20400 |
| 2020-06-06 |   3400 | 23800 |
| 2020-06-07 |   4900 | 28700 |
| 2020-06-08 |   8600 | 37300 |
| 2020-06-09 |   1700 | 39000 |
| 2020-06-10 |   5500 | 44500 |
+------------+--------+-------+