SELECT

@paid =

CASE WHEN day_of_week = 5 /*Sat*/ THEN CASE WHEN @age <= 10 THEN 300 ELSE 500 END

WHEN day_of_week = 6 /*Sun*/ THEN CASE WHEN @age <= 10 THEN 300 ELSE 700 END

WHEN DATEPART(HOUR, @time) >= 21 /*night*/ THEN CASE WHEN @age <= 10 THEN 200 ELSE 500 END

ELSE /*Mon-Fri,day*/ CASE WHEN @age <= 5 THEN 0 WHEN @age <= 10 THEN 100 ELSE 200 END

END

FROM (

--determine day_of_week using method that *always* works, regardless of language or date settings

SELECT DATEDIFF(DAY, 0, @date) % 7 AS day_of_week --0=Mon;1=Tue;etc.

) AS generated_data