存储过程MYSQL中的减法

我想看看你是否能帮我，我已经有很多次不使用Mysql了，现在我遇到了一些困难，我需要减去一个量，然后它就会累积起来，我在一个存储过程中这样做：

我希望它显示如下：

CREATE DEFINER=`root`@`localhost` PROCEDURE `balance`(
    in pclient int
)
BEGIN
    declare vbalance decimal(10,2);
    declare vamount decimal(10,2);
    SELECT amount + amount * percent into vbalance FROM credit where amount>0 and id_client= pclient;
    select 
        date, 
        if(amount>0,amount + amount * percent,amount) amount,
        vbalance + amount monto
    from 
        credit 
    where 
        id_client=pclient
        and id>=(select max(id) id from (SELECT * FROM credit where amount>0 and id_client=pclient) a);
        
END