计算当月第一天和最后一天

Question

我想在给定当前日期时间的情况下计算当月一周的第一个日期和最后一个日期。

例如，2017 年 12 月 1 日是第一天，2017 年 12 月 2 日是 12 月份那一周的最后一天。在一年中的同一周，2017 年 11 月 26 日是一周的第一天，并且 2017 年 11 月 30 日是上个月的最后一天。

所以如果今天是 2017 年 12 月 1 日，我应该从当前日期时间获取 01-02，而不是 26-02 范围。

PS: 我正在尝试在 Sqlite 查询中执行此操作。我想每周对一些值进行分组。星期几应该属于当月。因此这个要求。到目前为止，这是我的查询。

SELECT SUM(amount) as Y,
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '-'||strftime('%w', datetime(createdOn/1000, 'unixepoch'))||' day' )
||'-'||
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '+'||(6-strftime('%w', datetime(createdOn/1000, 'unixepoch')))||' day' )                 AS X
FROM my_table
GROUP BY strftime('%d', datetime(createdOn/1000, 'unixepoch'), '-'||strftime('%w', datetime(createdOn/1000, 'unixepoch'))||' day' )
||'-'||
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '+'||(6-strftime('%w', datetime(createdOn/1000, 'unixepoch')))||' day' )

如何实现；给定当前日期时间。

Answer 1

Common table expressions 用于保存中间结果：

WITH t1 AS (
  SELECT amount, date(createdOn / 1000, 'unixepoch', 'localtime') AS date
  FROM my_table
),
t2 AS (
  SELECT *,
         date(date, 'weekday 6') AS end_of_week,
         date(date, 'weekday 6', '-6 days') AS start_of_week
  FROM t1
),
t3 AS (
  SELECT *,
         strftime('%m', date         ) AS month,
         strftime('%m', start_of_week) AS sowk_month,
         strftime('%m', end_of_week  ) AS eowk_month,
         date(date, 'start of month') AS start_of_month,
         date(date, '+1 month', 'start of month', '-1 day') AS end_of_month
  FROM t2
),
t4 AS (
  SELECT *,
         CASE WHEN sowk_month = month THEN start_of_week
                                      ELSE start_of_month
         END AS week_in_month_start,
         CASE WHEN eowk_month = month THEN end_of_week
                                      ELSE end_of_month
         END AS week_in_month_end
  FROM t3
),
t5 AS (
  SELECT amount,
         week_in_month_start || '-' || week_in_month_end AS week_in_month
  FROM t4
)
SELECT SUM(amount) AS Y,
       week_in_month
FROM t5
GROUP BY week_in_month;

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