這個 SQL Script 是針對 Jack 的飯店業 BI
需要看到周變化，所以整理出來的 Script
BI 一般是看趨勢，理論上不會看到這麼細，但是要做當然是可以的


/*
  以年度共幾周為單位取日期區間(一年共 52 周)
  以下內容是 ChatGPT 的結果，令人驚豔
  
  Michael 20250604
*/

SET DATEFIRST 7;  -- 設定週日為每週第一天

WITH Weeks AS (
    SELECT 
        DATEADD(DAY, -(DATEPART(WEEKDAY, DATEFROMPARTS(2025, 1, 1)) - 1), DATEFROMPARTS(2025, 1, 1)) AS WeekStart
    UNION ALL
    SELECT 
        DATEADD(WEEK, 1, WeekStart)
    FROM Weeks
    WHERE DATEADD(WEEK, 1, WeekStart) <= DATEFROMPARTS(2025, 12, 31)
),
WeeksWithMonth AS (
    SELECT
        ROW_NUMBER() OVER (ORDER BY WeekStart) AS WeekNumber,
        WeekStart,
        DATEADD(DAY, 6, WeekStart) AS EndDate,
        MONTH(WeekStart) AS MonthNumber,
        DATENAME(MONTH, WeekStart) AS MonthName,
        YEAR(WeekStart) AS YearNumber
    FROM Weeks
    WHERE YEAR(WeekStart) = 2025 OR YEAR(DATEADD(DAY, 6, WeekStart)) = 2025
),
WeeksWithMonthRank AS (
    SELECT *,
        ROW_NUMBER() OVER (PARTITION BY YearNumber, MonthNumber ORDER BY WeekStart) AS WeekOfMonth
    FROM WeeksWithMonth
)
SELECT
    WeekNumber,
    WeekStart AS StartDate,
    EndDate,
    MonthName,
    MonthNumber,
    WeekOfMonth  -- ?? 當月第幾週
-- into Year_WeekData
FROM WeeksWithMonthRank
ORDER BY StartDate
OPTION (MAXRECURSION 100)






/*
  以下的寫法會將跨月的周，拆成 2 筆
  目的是如果要以月為單位看第幾周，就用下面的語法
*/

-- SET DATEFIRST 7;  -- 設定週日為一週的第一天（星期日）
SET DATEFIRST 1;  -- 設定週一為一週的第一天（星期一）

-- 產生所有週的開始日
WITH Weeks AS (
    SELECT 
        DATEADD(DAY, -(DATEPART(WEEKDAY, DATEFROMPARTS(2025, 1, 1)) - 1), DATEFROMPARTS(2025, 1, 1)) AS WeekStart
    UNION ALL
    SELECT 
        DATEADD(WEEK, 1, WeekStart)
    FROM Weeks
    WHERE DATEADD(WEEK, 1, WeekStart) <= DATEFROMPARTS(2025, 12, 31)
),

-- 加上 WeekNumber（全年第幾週）
WeeksWithNumber AS (
    SELECT 
        ROW_NUMBER() OVER (ORDER BY WeekStart) AS WeekNumber,
        WeekStart,
        DATEADD(DAY, 6, WeekStart) AS WeekEnd
    FROM Weeks
),

-- 將每週展開成7天
DaysInWeek AS (
    SELECT 
        W.WeekNumber,
        W.WeekStart,
        DATEADD(DAY, N.number, W.WeekStart) AS DayDate
    FROM WeeksWithNumber W
    JOIN master.dbo.spt_values N ON N.type = 'P' AND N.number BETWEEN 0 AND 6
    WHERE YEAR(DATEADD(DAY, N.number, W.WeekStart)) = 2025
),

-- 拆分週中涉及的每個月份的起訖日
WeekMonthSplit AS (
    SELECT
        WeekNumber,
        WeekStart,
        MONTH(DayDate) AS MonthNumber,
        DATENAME(MONTH, DayDate) AS MonthName,
        YEAR(DayDate) AS YearNumber,
        MIN(DayDate) AS StartDate,
        MAX(DayDate) AS EndDate
    FROM DaysInWeek
    GROUP BY WeekNumber, WeekStart, MONTH(DayDate), DATENAME(MONTH, DayDate), YEAR(DayDate)
),

-- 加上「當月第幾週」
FinalResult AS (
    SELECT *,
        ROW_NUMBER() OVER (PARTITION BY YearNumber, MonthNumber ORDER BY StartDate) AS WeekOfMonth
    FROM WeekMonthSplit
)

-- 輸出最終結果
SELECT
    ROW_NUMBER() OVER (ORDER BY StartDate) AS RecordID,
    WeekNumber,
    WeekStart,
    StartDate,
    EndDate,
    MonthName,
    MonthNumber,
    WeekOfMonth
-- into Year_WeekData
FROM FinalResult
ORDER BY StartDate
OPTION (MAXRECURSION 100)