Labor Day Vs. Thanksgiving

问题:

I am creating a calendar table for my warehouse. I will use this as a foreign key for all the date fields.

The code shown below creates the table and populates it. I was able to figure out how to find Memorial Day (last Monday of May) and Labor Day (first Monday of September).

SET NOCOUNT ON

DROP Table dbo.Calendar
GO
Create Table dbo.Calendar
(
    CalendarId              Integer NOT NULL,
    DateValue               Date    NOT NULL,
    DayNumberOfWeek         Integer NOT NULL,
    NameOfDay               VarChar (10) NOT NULL,
    NameOfMonth             VarChar (10) NOT NULL,
    WeekOfYear              Integer NOT NULL,
    JulianDay               Integer NOT NULL,
    USAIsBankHoliday        Bit     NOT NULL,
    USADayName              VarChar (100) NULL,
)
ALTER TABLE dbo.Calendar ADD CONSTRAINT
    DF_Calendar_USAIsBankHoliday DEFAULT 0 FOR USAIsBankHoliday
GO
ALTER TABLE dbo.Calendar ADD CONSTRAINT
    DF_Calendar_USADayName DEFAULT '' FOR USADayName
GO

Declare @StartDate  DateTime = '01/01/2000'
Declare @EndDate    DateTime = '01/01/2020'

While @StartDate < @EndDate
Begin
    INSERT INTO dbo.Calendar 
    (
        CalendarId, 
        DateValue, 
        WeekOfYear,
        DayNumberOfWeek,
        NameOfDay,
        NameOfMonth,
        JulianDay
    )
    Values 
    (
        YEAR (@StartDate) * 10000 + MONTH (@StartDate) * 100 + Day (@StartDate), --CalendarId
        @StartDate,                 -- DateValue
        DATEPART (ww, @StartDate),  -- WeekOfYear
        DATEPART (dw, @StartDate),  -- DayNumberOfWeek
        DATENAME (dw, @StartDate),  -- NameOfDay
        DATENAME (M, @StartDate),   -- NameOfMonth
        DATEPART (dy, @StartDate)   -- JulianDay
    )

    Set @StartDate += 1
End

--=========================== Weekends
-- saturday and sunday
UPDATE dbo.Calendar SET USAIsBankHoliday = 1, USADayName += 'Weekend, ' WHERE DayNumberOfWeek IN (1, 7) 


--=========================== Bank Holidays
-- new years day
UPDATE dbo.Calendar SET USAIsBankHoliday = 1, USADayName += 'New Year''s Day, '  WHERE (CalendarId % 2000) IN (101)

-- memorial day (last Monday in May)
UPDATE dbo.Calendar 
SET USAIsBankHoliday = 1, 
    USADayName += 'Memorial Day, '  
WHERE 1=1
AND CalendarId IN 
    (
        SELECT MAX (CalendarId)
        FROM dbo.Calendar 
        WHERE MONTH (DateValue) = 5 
        AND DATEPART (DW, DateValue)=2
        GROUP BY YEAR (datevalue)
    )

-- independence day
UPDATE dbo.Calendar SET USAIsBankHoliday = 1, USADayName += 'Independence Day, '  WHERE (CalendarId % 2000) IN (704)

-- labor day (first Monday in September)
UPDATE dbo.Calendar 
SET USAIsBankHoliday = 1, 
    USADayName += 'Labor Day, '  
WHERE 1=1
AND CalendarId IN 
    (
        SELECT MIN (CalendarId)
        FROM dbo.Calendar 
        WHERE MONTH (DateValue) = 9
        AND DATEPART (DW, DateValue)=2
        GROUP BY YEAR (datevalue)
    )

-- thanksgiving day (fourth Thursday in November)
UPDATE dbo.Calendar 
SET USAIsBankHoliday = 1, 
    USADayName += 'Thanksgiving Day, '  
WHERE 1=1
AND CalendarId IN 
    (
        SELECT Max (CalendarId)
        FROM dbo.Calendar 
        WHERE MONTH (DateValue) = 11
        AND DATEPART (DW, DateValue)=5
        GROUP BY YEAR (datevalue)
    )

-- christmas
UPDATE dbo.Calendar SET USAIsBankHoliday = 1, USADayName += 'Christmas Day, '  WHERE (CalendarId % 2000) IN (1225)

--=========================== Other named days
-- new years eve
UPDATE dbo.Calendar SET USADayName += 'New Year''s Eve, '  WHERE (CalendarId % 2000) IN (1231)

-- christmas eve
UPDATE dbo.Calendar SET USADayName += 'Christmas Eve, '  WHERE (CalendarId % 2000) IN (1224)

-- boxing day
UPDATE dbo.Calendar SET USADayName += 'Boxing Day, '  WHERE (CalendarId % 2000) IN (1226)

--=========================== Remove trailing comma
UPDATE dbo.Calendar SET USADayName = SubString (USADayName, 1, LEN (USADayName) -1) WHERE LEN (USADayName) > 2

SELECT * FROM dbo.Calendar

I am stumped on figuring out Thanksgiving day (Thursday of the last FULL week of November).

Edit: Correction based on comment by John Sauer

Thanksgiving is the fourth Thursday of November. However, upon checking several years, I find that it has turned out to also be the Thursday of the last full week of Nov.

回答1:

I am stumped on figuring out Thanksgiving day (Thursday of the last FULL week of November).

Last Saturday of November - 2

回答2:

Take the last Saturday of November, and subtract two days ;)

回答3:

WITH    cal AS
        (
        SELECT  CAST('2009-30-11' AS DATETIME) AS cdate
        UNION ALL
        SELECT  DATEADD(day, -1, cdate)
        FROM    cal
        WHERE   cdate >= '2009-01-11'
        )
SELECT  TOP 1 DATEADD(day, -2, cdate)
FROM    cal
WHERE   DATEPART(weekday, cdate) = 6

For the complex algorithms, it's sometimes better to find a matching date from a set than trying to construct an enormous single-value formula.

See this article in my blog for more detail:

• Checking event dates

回答4:

declare @thedate datetime
set @thedate = '11/24/2011'

select 1 
where datepart(dw, @thedate) = 5 and datepart(m, @thedate) = 11 AND (datepart(dd, @thedate) - 21) between 0 and 6

Is the date a Thursday in November and is there less than a week remaining.