带有"默认值"的SQL GROUP BY

Question

我正在尝试SELECT使用GROUP BY子句创建语句,该子句应返回"默认值".

想象一下以下简单的MySQL表:

CREATE TABLE `tracker` (
  `id` INTEGER PRIMARY KEY auto_increment,
  `date` DATETIME NOT NULL,
  `customer_id` INTEGER NOT NULL
);

该表只包含一条记录:

INSERT INTO `tracker` (`date`, `customer_id`) VALUES('2010-05-03', 1);

在病房之后,我正在执行以下SQL查询:

SELECT DATE(`date`), COUNT(customer_id) FROM tracker
WHERE DATE(`date`) >= '2010-05-01' AND DATE(`date`) <= '2010-05-05'
GROUP BY DATE(`date`) ORDER BY DATE(`date`);

并获得预期的结果集:

+----+---------------------+-------------+
| id | date                | customer_id |
+----+---------------------+-------------+
|  1 | 2010-05-10 00:00:00 |           1 |
+----+---------------------+-------------+

但是,我希望结果集看起来像这样:

+--------------+--------------------+
| DATE(`date`) | COUNT(customer_id) |
+--------------+--------------------+
| 2010-05-01   |                  0 |
| 2010-05-02   |                  0 |
| 2010-05-03   |                  1 |
| 2010-05-04   |                  0 |
| 2010-05-05   |                  0 |
+--------------+--------------------+

有可能实现这种行为吗？

Answer 1

您可以构建一个范围内有效日期的临时表，然后将其合并到您的查询中 - 这是我可以立即看到的唯一前进方法......

马丁