I am not sure if you are looking to do the same case in the where clause to compare the product and order load date with the start and end date
where loaddate between @Start and @END
the above where can be written as
loaddate >= @Start and loaddate<= @END
the below query migt be help for you , but if u could provide exact requrment with the sample data and the table structure , could help in writing
where @END>loaddate and @Start<loaddate
where @End >=
CASE WHEN a.loadate >= b.loaddate
THEN a.loaddate
ELSE b.loaddate
END
and
@Start <=
CASE WHEN a.loadate >= b.loaddate
THEN a.loaddate
ELSE b.loaddate
END