One of my first 10 blog posts explained why some formulas could be totaled and others could not. Two of the things that prevent a formula from being summarized (totaled) are if the formula itself refers to a subtotal, or if it uses the functions Previous() or Next().

But I was reminded recently that both of these types of formulas can be summarized in a Cross-tab. Take these two formula examples:

// Rebate:
if Sum ({Orders.Order Amount}, {Customer.Customer Name}) > 25000
then {Orders.Order Amount} *.05
else 0

//Days Between Orders:
if {Customer.Customer Name} = Previous({Customer.Customer Name})
then {Orders.Order Date} - Previous ({Orders.Order Date})
else val({@null})

If I wanted to do a grand total of my rebates or an average of the days between orders I wouldn’t be able to use normal summary functions.   Even Crystal running total fields won’t work with these. In most cases people would resort to using variable to accumulate these totals. However, both of these formulas can be summarized using a cross-tab. You could do a simple cross-tab with a single cell to show the grand total and no row or column fields.  Or you could do breakdowns by other fields.

Not only does this save you dealing with variables, but a cross-tab can put these totals on the first page (Report Header), while variables will only be complete on the last page (Report Footer).  One more reason to use my favorite objects.