Sum of two rows

Hi,

this might be an obvious thing, but still I'm biting on this for some time:

Let's pretend  I want to have a table with 3 columns.
The first and second should each hold an integer value, the third should
hold the sum of column1 + column2 as an integer.

The idea behind this table should be that the sum is automatically
updated, each time I change one of the values in either of the first two
columns.

Best regards,
alex

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Institut fuer Geographie und Regionalforschung
Universitaet Wien
Kartografie und Geoinformation

Departement of Geography and Regional Research
University of Vienna
Cartography and GIS

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