一、获得给定月份的周日数

根据给定的某个日期，计算这个月份的周日的天数。
根据系统变量@@DATEFIRST的值，判断周日的序号为【DatePart(WEEKDAY,RQ)= (07-@@DateFirst) % 7 + 1】。下面列出了周日、周一…周六的公式

下面是获得周日的SQL语句，SQL语句采用了嵌套循环的方式来获取数据

DECLARE @Day SmallDateTime
SET @Day = DateAdd(MM, DateDiff(MM,0,’2019-11-21′), 0)

;WITH Temp AS
( SELECT @Day AS RQ UNION ALL
SELECT RQ+1
FROM TEMP WHERE DateDiff(Month,RQ+1,@Day) = 0
)
SELECT
RN = Row_Number() Over(ORDER BY RQ),
RQ
FROM Temp WHERE DatePart(WEEKDAY,RQ)= (07-@@DateFirst) % 7 + 1