如果列中的数字为负数，则显示为正数，否则显示数字

I have a [Preko]column in a query that is calculating the difference between two columns.If the number is negative,I need to show it positive,and if it is positive,it should stay the same.I can't use ABS in this one.I tried with the case,but it didn't work. The problem I am getting is that column Preko is invalid.I have a [Preko]column in a query that is calcu