MySQL将日期范围转换为每年单行/计数天？

Question

我正在寻找一种解决方案，以每年计算一个日期范围内的天数。 我的桌子看起来像这样：

+----+-----------+------------+------------+
| id | source_id | start_date | end_date   |
+----+-----------+------------+------------+
|  1 |         1 | 2015-11-01 | 2017-01-31 |
+----+-----------+------------+------------+

现在我要计算一下之间的天数。 使用DATEDIFF（）可以很容易地完成，但是每年如何做呢？

我尝试了一种临时工。 转换为单行以执行计数和分组操作：

+----+-----------+------------+------------+
| id | source_id | start_date | end_date   |
+----+-----------+------------+------------+
|  1 |         1 | 2015-11-01 | 2015-12-31 |
+----+-----------+------------+------------+
|  1 |         1 | 2016-01-01 | 2016-12-31 |
+----+-----------+------------+------------+
|  1 |         1 | 2017-01-01 | 2017-01-31 |
+----+-----------+------------+------------+

编辑：所需的输出应为：

+-----------+------+------+
| source_id | year | days |
+-----------+------+------+
|         1 | 2015 |   60 |
+-----------+------+------+
|         1 | 2016 |  365 |
+-----------+------+------+
|         1 | 2017 |   30 |
+-----------+------+------+

因此，可以汇总按source_id和year分组的所有天。

在MySQL中有简单的方法吗？

Answer 1

创建另一个列出所有年份的表：

CREATE TABLE years (
    year_start DATE,
    year_end DATE
);
INSERT INTO years VALUES 
    ('2015-01-01', '2015-12-31'), 
    ('2016-01-01', '2016-12-31'),
    ('2017-01-01', '2017-12-31');

然后你可以加入这张桌子

SELECT t.source_id, YEAR(y.year_start) AS year, DATEDIFF(LEAST(year_end, end_date), GREATEST(year_start, start_date)) AS day_count
FROM yourTable AS t
JOIN years AS y 
    ON y.year_start BETWEEN t.start_date AND t.end_date
    OR y.year_end BETWEEN t.start_date AND t.end_date

演示

如果您不想创建一个真实的表，可以使用一个子查询来动态创建它：

SELECT t.source_id, YEAR(y.year_start) AS year, DATEDIFF(LEAST(year_end, end_date), GREATEST(year_start, start_date)) AS day_count
FROM yourTable AS t
JOIN (SELECT CAST('2015-01-01' AS DATE) AS year_start, CAST('2015-12-31' AS DATE) AS year_end
      UNION
      SELECT CAST('2016-01-01' AS DATE) AS year_start, CAST('2016-12-31' AS DATE) AS year_end
      UNION
      SELECT CAST('2017-01-01' AS DATE) AS year_start, CAST('2017-12-31' AS DATE) AS year_end
    ) AS y
    ON y.year_start BETWEEN t.start_date AND t.end_date
    OR y.year_end BETWEEN t.start_date AND t.end_date

演示

Answer 2

我找到了其他代码片段，并且将两者结合在一起。 它比解决方案更能解决问题，但对于我的目的来说效果很好。

SELECT r.source_id, 
   YEAR(y.year_start) AS year,
   DATEDIFF(LEAST(year_end, end_date), GREATEST(year_start, start_date)) AS day_count,
   r.start_date,
   r.end_date
  FROM ranges AS r
  JOIN (
      SELECT @i:= @i + 1 AS YEAR,
             CAST(CONCAT(@i, '-01-01') AS DATE) AS year_start,
             CAST(CONCAT(@i, '-12-31') AS DATE) AS year_end
        FROM INFORMATION_SCHEMA.COLLATION_CHARACTER_SET_APPLICABILITY,
             (SELECT @i:= 1899) AS i
     ) AS y
    ON r.start_date >= y.year_start AND r.start_date <= y.year_end
    OR r.end_date >= y.year_start AND r.end_date <= y.year_end;

我认为，表INFORMATION_SCHEMA.COLLATION_CHARACTER_SET_APPLICABILITY只是进行迭代的一种解决方法。 不好，但是也许有人需要这样的东西。