I think issue is with datatype of CurrentStock & MinimumRequired.
check for datatype.
for eg.
below case will say 2 is greater then 10
declare @a varchar(10)
declare @b varchar(10)
set @a='10'
set @b='2'
select case when @a >@b then @a +' is greater' when @a = @b then 'Both are equal'
else @b +' is greater' end as Greater
output:
Greater
2 is greater