Mysql为每个月份的日期选择计数

Question

我们说我有一张如下表：

date_upload|url_upload|status_upload
2017-11-01 |www.com   |verified
2017-12-01 |www.com   |verified
2017-13-01 |www.com   |verified
2017-11-01 |www.com   |verified

我希望得到这样的结果：

date_upload |count_upload
2017-01-01  | 0
2017-02-01  | 0
..........  | 0
2017-11-01  | 2
2017-12-01  | 1
2017-13-01  | 1
2017-14-01  | 0
..........  | 0
2017-31-01  | 0

结果应该返回本月每个日期的计数，尽管我的记录只有4个。

Answer 1

使用日历表：

SELECT t1.date, COUNT(t2.date_upload) AS count_upload
FROM
(
    SELECT '2017-01-01' AS date UNION ALL
    SELECT '2017-01-02' UNION ALL
    SELECT '2017-01-03' UNION ALL
    ...
    SELECT '2017-01-31'
) t1
LEFT JOIN yourTable t2
    ON t1.date = t2.date_upload
GROUP BY
    t1.date;

在实践中，名为t1的子查询可以替换为包含这些日期的真实日历表。