Calculating the sum of the column values in a straight table
If you have hard-coded your expression (columns), then you can do a sum over them by calling their label names. Otherwise, if you used a dynamic label, you can use the column function, e.g. column(1) + column(2) + ..., where column(N) is the Nth expression stated from top to bottom in the expression tab.
If this doesn't answer your question, do you have a sample QVW to see what you're trying to do?