用mysql计算余额

Question

我有一个包含以下数据的表:

ID      In       Out 
1      100.00    0.00   
2       10.00    0.00   
3        0.00   70.00    
4        5.00    0.00    
5        0.00   60.00   
6       20.00    0.00     

现在我需要一个查询,它给出了以下结果:

ID      In       Out    Balance
1      100.00    0.00   100.00
2       10.00    0.00   110.00
3        0.00   70.00    40.00
4        5.00    0.00    45.00
5        0.00   60.00   -15.00
6       20.00    0.00     5.00

是否可以使用一个查询执行此操作,而无需使用触发器或存储过程？

Answer 1

简短的回答,是的

更长的答案,你可以使用一个变量来计算它,因为它迭代行,即

SELECT 
    `table`.`ID`,
    `table`.`In`,
    `table`.`Out`,
    @Balance := @Balance + `table`.`In` - `table`.`Out` AS `Balance`
FROM `table`, (SELECT @Balance := 0) AS variableInit
ORDER BY `table`.`ID` ASC

在, (SELECT @Balance := 0) AS variableInit你开始之前@Balance被初始化为0保证.然后对于每一行,它将@Balance设置为@Balance + In - Out,然后输出计算的值.

另外值得确定ORDER是否一致,否则Balance会根据返回行的顺序而有所不同.例如,如果您想将其重新排序到前面,则可以将其用作子查询,然后外部查询处理计算值,从而确保平衡保持正确,即

SELECT
    `balanceCalculation`.`ID`,
    `balanceCalculation`.`In`,
    `balanceCalculation`.`Out`,
    `balanceCalculation`.`Balance`
FROM (
    SELECT 
        `table`.`ID`,
        `table`.`In`,
        `table`.`Out`,
        @Balance := @Balance + `table`.`In` - `table`.`Out` AS `Balance`
    FROM `table`, (SELECT @Balance := 0) AS variableInit
    ORDER BY `table`.`ID` ASC
) AS `balanceCalculation`
ORDER BY `balanceCalculation`.`ID` DESC