hi all,

  i have a product table ,i already achieve subtotal function field ,but now i want achieve total a function.
my subtotal function is:{Product_Tb.Product Quantity} * {Product_Tb.Product Price}
then how  will  to total a function achieve,
i try below "total"function:
sum({Product_Tb.Product Quantity} * {Product_Tb.Product Price}
)
but crystal reports prompt  error:here need one the field

thanks in advance.