獲知某一年的母親節，父親節和感恩節日期

完成這個要求之前，可以先參考另外一個函數《獲取當月的天數列表》https://www.cnblogs.com/insus/p/10837900.html：

然後要知道標題三個節日的常識，母親節在每年5月份的第二個星期天，父親節在每年6月份的第三個星期天，而感恩節是在每年的11月份第四個星期的星期四。

知道這些常識就好辦了。

寫一個SQL的自定義函數：

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

-- =============================================
-- Author:      Insus.NET
-- Create date: 2019-05-12
-- Update date: 2019-05-12
-- Description: 獲取節日日期
-- =============================================
CREATE FUNCTION [dbo].[svf_Festivals]
(
    @StartYear INT,
    @EndYear INT
)
RETURNS @tempTable TABLE([ID] INT IDENTITY(1,1) PRIMARY KEY,[Year] [INT] NOT NULL,[Mother's Day] [DATETIME] NULL,[Father's Day] [DATETIME] NULL,[Thanksgiving Day] DATETIME)
AS
BEGIN   
    WHILE @StartYear <= @EndYear
    BEGIN
        INSERT INTO @tempTable ([Year]) VALUES(@StartYear)      

        UPDATE @tempTable SET [Mother's Day] = (
            SELECT [Date] FROM (
                SELECT ROW_NUMBER() OVER (ORDER BY [Date] ASC) AS [RowNumber], [Date] FROM [dbo].[tvf_DaysOfMonth](CAST(@StartYear AS NVARCHAR(4)) + '-05-01')
                WHERE DATENAME(dw,[Date]) = 'Sunday') AS md 
            WHERE [RowNumber] = 2)
        WHERE [Year] = @StartYear

        UPDATE @tempTable SET [Father's Day] = (
            SELECT [Date] FROM (
                SELECT ROW_NUMBER() OVER (ORDER BY [Date] ASC) AS [RowNumber], [Date] FROM [dbo].[tvf_DaysOfMonth](CAST(@StartYear AS NVARCHAR(4)) + '-06-01')
                WHERE DATENAME(dw,[Date]) = 'Sunday') AS fd 
            WHERE [RowNumber] = 3)
        WHERE [Year] = @StartYear
        
        UPDATE @tempTable SET [Thanksgiving Day] = (
            SELECT [Date] FROM (
                SELECT ROW_NUMBER() OVER (ORDER BY [Date] ASC) AS [RowNumber], [Date] FROM [dbo].[tvf_DaysOfMonth](CAST(@StartYear AS NVARCHAR(4)) + '-11-01')
                WHERE DATENAME(dw,[Date]) = 'Thursday') AS td 
            WHERE [RowNumber] = 4)
        WHERE [Year] = @StartYear

        SET @StartYear = @StartYear + 1
    END  

    RETURN
END
GO

下麵是列出2019至2025年所有以上三個節日的日期，幫忙檢查一下，是否正確？