Tables usually need totals. In Tableau they live under Analysis > Totals:
- Show Column Grand Totals adds a Grand Total row at the bottom: the total of each column.
- Show Row Grand Totals adds a Grand Total column on the right: the total of each row.
- Add All Subtotals adds a Total row after each group of an outer dimension, for example after the sub-categories of each category.
You can also drag Totals from the Analytics pane onto the view.
Tableau doesn't add up the numbers you see. It goes back to the rows and aggregates them again with the measure's own aggregation. For SUM that's the same thing. For AVG it's not: the grand total of AVG(Sales) is the average of all order lines, not the average of the averages shown above it. Keep that in mind when a total looks "wrong".