Updating tables from file

This is probably more a novice SQL question than a Postgres question, but I
thought I'd try here first:

I have a table with data in it that I would like to update it with similar
data in a file. The fields in both are laid out like this:
username {PK} data1 int2 data2 int data3 int3

For each username, I want to sum the corresponding integer fields and have
the resulting data placed into a second table. How can I script this in
Postgres?

Thanks!

Lorenzo Thurman lthurman(at)northwestern(dot)edu
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