A UDF from Robyn Page’s SQL Server DATE/TIME Workbench

gistfile1.txt

 IF OBJECT_ID (N'NthDayOfWeekOfMonth') IS NOT NULL
           DROP FUNCTION NthDayOfWeekOfMonth
        GO
        
        CREATE FUNCTION NthDayOfWeekOfMonth (
        @TheYear CHAR(4), --the year as four characters (e.g. '2014')
        @TheMonth CHAR(3), --in english (Sorry to our EU collegues) e.g. Jun, Jul, Aug
        @TheDayOfWeek CHAR(3), -- one of Mon, Tue, Wed, Thu, Fri, Sat, Sun
        @Nth INT) --1 for the first date, 2 for the second occurence, 3 for the third
        RETURNS DATETIME
        WITH EXECUTE AS CALLER
        AS
        BEGIN
        RETURN DATEADD(MONTH, DATEDIFF(MONTH, 0, CONVERT(date,'1 '+@TheMonth+' '+@TheYear,113)), 0)+ (7*@Nth)-1
                -(DATEPART (Weekday, DATEADD(MONTH, DATEDIFF(MONTH, 0, CONVERT(date,'1 '+@TheMonth+' '+@TheYear,113)), 0))
                +@@DateFirst+(CHARINDEX(@TheDayOfWeek,'FriThuWedTueMonSunSat')-1)/3)%7
        END 
        --https://www.red-gate.com/simple-talk/sql/learn-sql-server/robyn-pages-sql-server-datetime-workbench/