Labor Day Vs. Thanksgiving - sql-server

Question

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.

Answer 1

I am stumped on figuring out Thanksgiving day (Thursday of the last FULL week of November).
Last Saturday of November - 2

Answer 2

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

Answer 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

Answer 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.

Answer 5

We use a neat Scalar-valued Function in our database that we can call to determine whether or not a date is a NonWorkDay. We manually add special dates for Observed Holidays.
Create Function:
CREATE FUNCTION [dbo].[NonWorkDay](#date as DATETIME)
RETURNS bit
AS
BEGIN
if #date is not null
begin
-- Weekends
if DATEPART(weekday, #date)=1 return 1 --Sunday
if DATEPART(weekday, #date)=7 return 1 --Saturday
-- JAN
if month(#date)=1 AND day(#date)=1 return 1 -- New Years Day
-- MAY
if month(#date)=5 and DATEPART(weekday, #date)=2 and day(#date)>24 and day(#date)<=31 return 1 --Memorial Day
-- JULY
if month(#date)=7 AND day(#date)=4 return 1 -- July 4th
-- SEP
if month(#date)=9 and DATEPART(weekday, #date)=2 and day(#date)<=7 return 1--Labor Day
-- NOV
if month(#date)=11 and DATEPART(weekday, #date)=5 and day(#date)>21 and day(#date)<=28 return 1--Thanksgiving
if month(#date)=11 and DATEPART(weekday, #date)=6 and day(#date)>22 and day(#date)<=29 return 1 -- Black Friday
-- DEC
if month(#date)=12 AND day(#date)=24 return 1 -- Christmas Eve
if month(#date)=12 AND day(#date)=25 return 1 -- Christmas
if month(#date)=12 AND day(#date)=31 return 1 -- NYE
-- Office Closed for Observed Holiday Dates
if month(#date)=7 AND day(#date)=5 AND year(#date)=2021 return 1 -- 4th of July Observed for 2021
if month(#date)=12 AND day(#date)=26 AND year(#date)=2022 return 1 -- Christmas Day observed for 2022
if month(#date)=1 AND day(#date)=2 AND year(#date)=2023 return 1 -- New Years Day observed for 2023
if month(#date)=7 AND day(#date)=3 AND year(#date)=2026 return 1 -- 4th of July Observed for 2026
if month(#date)=7 AND day(#date)=5 AND year(#date)=2027 return 1 -- 4th of July Observed for 2027
end
return 0
END
GO
Call Function:
IF [dbo].[NonWorkDay](Getdate())= 0 -- If (not a NonWorkDay -ie not Sat or Sun)