在 MariaDb 查询中，给定年份、月份和星期，如何获取一周中的第一天的星期几？

Question

是否有可能在给定年份、月份和星期的情况下获得一周的第一个日期的 DAYOFMONTH？
请注意，一周的第一个日期也可能是前一个月甚至是前一年。

我知道这可以通过编程方式实现，至少使用 java.time、TemporalFields 等。但我想在 sql 查询级别上执行此操作，因为当涉及周时，该过程涉及两个额外参数，即 DayOfWeek这被认为是一周的第一天和一个月内一周的最少天数。 如果 sql 和 api 上的配置不完全相同，这可能会导致不同的结果。

使用 DayOfMonth.Monday 和第一周的最少天数的示例：1，
就 sql 而言，它应该是WEEK MariaDb function的模式 7。

Given Year: 2020 Given Month: 1 Given Week: 1 Result: 30
Given Year: 2020 Given Month: 1 Given Week: 2 Result: 6
Given Year: 2020 Given Month: 1 Given Week: 3 Result: 13
Given Year: 2020 Given Month: 1 Given Week: 4 Result: 20
Given Year: 2020 Given Month: 1 Given Week: 5 Result: 27
Given Year: 2020 Given Month: 2 Given Week: 5 Result: 27
Given Year: 2020 Given Month: 2 Given Week: 6 Result: 3
Given Year: 2020 Given Month: 2 Given Week: 7 Result: 10
Given Year: 2020 Given Month: 2 Given Week: 8 Result: 17
Given Year: 2020 Given Month: 2 Given Week: 9 Result: 24
Given Year: 2020 Given Month: 3 Given Week: 9 Result: 24
Given Year: 2020 Given Month: 3 Given Week: 10 Result: 2
Given Year: 2020 Given Month: 3 Given Week: 11 Result: 9
Given Year: 2020 Given Month: 3 Given Week: 12 Result: 16
Given Year: 2020 Given Month: 3 Given Week: 13 Result: 23
Given Year: 2020 Given Month: 3 Given Week: 14 Result: 30
Given Year: 2020 Given Month: 4 Given Week: 14 Result: 30
Given Year: 2020 Given Month: 4 Given Week: 15 Result: 6
Given Year: 2020 Given Month: 4 Given Week: 16 Result: 13
Given Year: 2020 Given Month: 4 Given Week: 17 Result: 20
Given Year: 2020 Given Month: 4 Given Week: 18 Result: 27
Given Year: 2020 Given Month: 5 Given Week: 18 Result: 27
Given Year: 2020 Given Month: 5 Given Week: 19 Result: 4
Given Year: 2020 Given Month: 5 Given Week: 20 Result: 11
Given Year: 2020 Given Month: 5 Given Week: 21 Result: 18
Given Year: 2020 Given Month: 5 Given Week: 22 Result: 25
Given Year: 2020 Given Month: 6 Given Week: 23 Result: 1
Given Year: 2020 Given Month: 6 Given Week: 24 Result: 8
Given Year: 2020 Given Month: 6 Given Week: 25 Result: 15
Given Year: 2020 Given Month: 6 Given Week: 26 Result: 22
Given Year: 2020 Given Month: 6 Given Week: 27 Result: 29
Given Year: 2020 Given Month: 7 Given Week: 27 Result: 29
Given Year: 2020 Given Month: 7 Given Week: 28 Result: 6
Given Year: 2020 Given Month: 7 Given Week: 29 Result: 13
Given Year: 2020 Given Month: 7 Given Week: 30 Result: 20
Given Year: 2020 Given Month: 7 Given Week: 31 Result: 27
Given Year: 2020 Given Month: 8 Given Week: 31 Result: 27
Given Year: 2020 Given Month: 8 Given Week: 32 Result: 3
Given Year: 2020 Given Month: 8 Given Week: 33 Result: 10
Given Year: 2020 Given Month: 8 Given Week: 34 Result: 17
Given Year: 2020 Given Month: 8 Given Week: 35 Result: 24
Given Year: 2020 Given Month: 8 Given Week: 36 Result: 31
Given Year: 2020 Given Month: 9 Given Week: 36 Result: 31
Given Year: 2020 Given Month: 9 Given Week: 37 Result: 7
Given Year: 2020 Given Month: 9 Given Week: 38 Result: 14
Given Year: 2020 Given Month: 9 Given Week: 39 Result: 21
Given Year: 2020 Given Month: 9 Given Week: 40 Result: 28
Given Year: 2020 Given Month: 10 Given Week: 40 Result: 28
Given Year: 2020 Given Month: 10 Given Week: 41 Result: 5
Given Year: 2020 Given Month: 10 Given Week: 42 Result: 12
Given Year: 2020 Given Month: 10 Given Week: 43 Result: 19
Given Year: 2020 Given Month: 10 Given Week: 44 Result: 26
Given Year: 2020 Given Month: 11 Given Week: 44 Result: 26
Given Year: 2020 Given Month: 11 Given Week: 45 Result: 2
Given Year: 2020 Given Month: 11 Given Week: 46 Result: 9
Given Year: 2020 Given Month: 11 Given Week: 47 Result: 16
Given Year: 2020 Given Month: 11 Given Week: 48 Result: 23
Given Year: 2020 Given Month: 11 Given Week: 49 Result: 30
Given Year: 2020 Given Month: 12 Given Week: 49 Result: 30
Given Year: 2020 Given Month: 12 Given Week: 50 Result: 7
Given Year: 2020 Given Month: 12 Given Week: 51 Result: 14
Given Year: 2020 Given Month: 12 Given Week: 52 Result: 21
Given Year: 2020 Given Month: 12 Given Week: 53 Result: 28

Answer 1

我确实感觉到拥有它的重要性，但我没有在 MySQL/MariaDB 中找到任何可以直接使用的内置 function（如WEEK()等，如果有的话）。 在我的例子中，我使用自定义查询来生成周数，到目前为止，下面的查询一直在返回正确的周数：

SELECT mnd AS 'StartDate', 
       mxd AS 'EndDate', 
       ROW_NUMBER() OVER (PARTITION BY  YEAR(mxd) ORDER BY mnd) AS 'WeekNo' 
FROM
(SELECT MIN(dt) AS mnd,MAX(dt) AS mxd, nom FROM
 (SELECT dt, num , CEIL(num/7) AS nom FROM
  (SELECT DATE_FORMAT(CONCAT_WS('-',yr,mnt,dy),'%Y-%m-%d') AS dt, 
          ROW_NUMBER() OVER (ORDER BY dt) AS num 
      FROM
      /*Query to generate date in MariaDB*/
      (SELECT LPAD(seq,2,0) AS dy FROM seq_1_to_31) a,
      (SELECT LPAD(seq,2,0) AS mnt FROM seq_1_to_12) b,
      (SELECT seq AS yr FROM seq_2018_to_2023) c
      /*-------------------------*/
HAVING dt IS NOT NULL ORDER BY dt) V ) W 
GROUP BY nom) Q;

演示小提琴在这里

我首先在子查询中执行了ROW_NUMBER()然后使用该结果除以 7（每周 7 天），上限为 function（ CEIL() ）。 然后执行另一个查询，以在日期内使用MIN()和MAX()按上限 function 的结果进行分组。 我在EndDate的年份用PARTITION对查询做了另一个ROW_NUMBER() function 。 除了最重要的事情之外，所有这些都是第一年的 select，其中 1/January = Monday； 在上面的示例中，01/01/2018 是星期一。