Mysql 如何保持交易的连续余额，并在交易后获得金额

我必须编写一个查询，使用一个变量列出ID为1的客户执行的按日期排序的所有交易。变量应保持一个运行余额，以显示每次交易后客户的新余额。最终输出应给出日期、交易金额和交易后的当前余额

表格

+--------------+------------------+------+-----+-------------------+-----------------------------+
| Field        | Type             | Null | Key | Default           | Extra                       |
+--------------+------------------+------+-----+-------------------+-----------------------------+
| customer_id  | int(10) unsigned | YES  | MUL | NULL              |                             |
| last_created | timestamp        | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| amount       | decimal(6,2)     | NO   |     | NULL              |                             |
+--------------+------------------+------+-----+-------------------+-----------------------------+

查询

SELECT last_created, amount , sum(amount) as moneyspent FROM transactions where 
customer_id = 1   ORDER BY  last_created;

SET @total = 0; 
SELECT last_transaction, amount ,@total := @total + amount AS runningtotal 
FROM sakila_payment 
ORDER BY last_transaction;