Question

例如我有：

CREATE TABLE application (
`id` INT(11) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
`month` VARCHAR(255) NOT NULL,
`amount` DECIMAL(9,2) NOT NULL)
;
INSERT INTO application 
(`id`, `month`, `amount`)
VALUES 
(1, 'january', 2000.00),
(2, 'february', 1000.00),
(3, 'january', 3000.00),
(4, 'january', 5000.00)
;

然后我运行查询：

SELECT SUM(`amount`) as sum FROM application WHERE month IN ('january', 'february', 'march') GROUP BY `month`;

我得到了结果：

  month      sum
___________________
january  | 10000.00
february | 1000.00

这是查询本应该做的，但是我正在寻找这个结果：

  month      sum
___________________
january  | 10000.00
february | 1000.00
march    | 0.00

我怎样才能做到这一点？

如果有人需要清晰，请不要只是问一下，如果可以，我会更精确。

欢呼声

Answer 1

SELECT m.mname, SUM(ISNULL(a.`amount`,0)) as sum 
FROM 
(
select 'january' as mname union all
select 'february' as mname union all
select 'march' as mname 
) m LEFT JOIN application a on a.`month` = m.mname 
GROUP BY a.`month`

mySQL - 如果找不到字段，则返回0作为聚合结果

1 个答案: