Populate Calendar Table (T-SQL)

--Update NULL fields in Calendar table

UPDATE AdventureWorks2019.dbo.Calendar
SET
DayOfWeekNumber = DATEPART(WEEKDAY,DateValue),
DayOfWeekName = FORMAT(DateValue,'dddd'),
DayOfMonthNumber = DAY(DateValue),
MonthNumber = MONTH(DateValue),
YearNumber = YEAR(DateValue)


SELECT * FROM AdventureWorks2019.dbo.Calendar



UPDATE AdventureWorks2019.dbo.Calendar
SET
WeekendFlag =
    CASE
        WHEN DayOfWeekNumber IN(1,7) THEN 1
        ELSE 0
    END


SELECT * FROM AdventureWorks2019.dbo.Calendar



UPDATE AdventureWorks2019.dbo.Calendar
SET
HolidayFlag =
    CASE
        WHEN DayOfMonthNumber = 1 AND MonthNumber = 1 THEN 1
        ELSE 0
    END


SELECT * FROM AdventureWorks2019.dbo.Calendar


--Use Calendar table in a query


SELECT
A.*

FROM AdventureWorks2019.Sales.SalesOrderHeader A
    JOIN AdventureWorks2019.dbo.Calendar B
        ON A.OrderDate = B.DateValue

WHERE B.WeekendFlag = 1