MySQL 计算 table 中两个日期之间的星期几

Question

我的预订 table 包含以下列：

id, start_date, end_date

我想知道在我的数据集中哪几天的预订最多。

我可以在开始日期上使用 dayofweek() 并以此为分组，并使用计数 (*)。但我还想包括预订开始和结束之间的天数。

示例输出为

dayofweek     count(*)
1             1
2             1
3             1
4             2
5             3
6             3
7             1

下一组

id       start_date          end_date
1        2017-10-01          2017-10-07
2        2017-10-04          2017-10-07
3        2017-10-06          2017-10-08

Answer 1

您可以通过递归 table:

WITH cte AS
(
    SELECT DATE_ADD(start_date INTERVAL 1 DAY) AS date, end_date, DAYOFWEEK(start_date) AS dw from bookings
    UNION ALL 
    SELECT DATE_ADD(start_date INTERVAL 1 DAY), end_date, DAYOFWEEK(date)
    FROM cte WHERE date <= end_date
)
SELECT COUNT(*), dw FROM cte GROUP BY dw

Answer 2

我假设您希望知道从开始到结束期间每个日期有多少房间已入住。这里的"trick" 是start/end 之间的长周期将重复and/or 的一天或一周，一周的结束日可能小于一周的开始日。所以，我有：

生成了一个包含 100,000 个日期的列表（每行 1 个）
在您的 table
将每个连接的行转换为要计算的星期几
left 连接到 1 到 7 的列表，并计算第 3 步的行数

注意：如果 end_date 是 "check out date"，则可能需要从每条记录中扣除 1 天以进行补偿（下面没有这样做）。

可在 SQL Fiddle

此处查看此方法

MySQL 5.6 架构设置:

CREATE TABLE Table1
    (`id` int, `start_date` datetime, `end_date` datetime)
;

INSERT INTO Table1
    (`id`, `start_date`, `end_date`)
VALUES
    (1, '2017-09-21 00:00:00', '2017-10-07 00:00:00'), ## added this row
    (1, '2017-10-01 00:00:00', '2017-10-07 00:00:00'),
    (2, '2017-10-04 00:00:00', '2017-10-07 00:00:00'),
    (3, '2017-10-06 00:00:00', '2017-10-08 00:00:00')
;

查询:

set @commence := str_to_date('2000-01-01','%Y-%m-%d')

select
    w.dy
  , count(t.wdy)
from (
      select 1 dy union all select 2 dy union all select 3 dy union all
      select 4 dy union all select 5 dy union all select 6 dy union all select 7 dy
      ) w
left join (
      select DAYOFWEEK(cal.dy) wdy
      from (
              select adddate( @commence ,t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) dy 
              from  (     select 0 i union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) t0 
              cross join (select 0 i union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) t1 
              cross join (select 0 i union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) t2 
              cross join (select 0 i union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) t3 
              cross join (select 0 i union all select 1 union all select 2 union all select 3 union all select 4 union all select 5 union all select 6 union all select 7 union all select 8 union all select 9) t4
          ) cal
      INNER JOIN Table1 t on cal.dy between t.start_date and t.end_date
      ) t on w.dy = t.wdy
group by
    w.dy

Results:

| dy | count(t.wdy) |
|----|--------------|
|  1 |            4 |
|  2 |            3 |
|  3 |            3 |
|  4 |            4 |
|  5 |            5 |
|  6 |            6 |
|  7 |            6 |

另请参阅：How to get list of dates between two dates in mysql select query 其中接受的答案是交叉联接集的基础，该交叉联接生成从指定日期开始的 100,000 个日期。然而，我修改了它的语法（显式交叉连接语法），一个参数作为起点，并使用 union all 提高效率。

MySQL 计算 table 中两个日期之间的星期几

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