new calculated column

Hi;

I've got a table with two fields and about 3000 rows, the second one is a
character field, what can have about twenty different values; of course these
values are repeated a lot of times in the table. I need to create a new
column of type integer, whose value depens on the character fields. The
values of the new column are not important, the important thing is who can I
create this column and assign a different integer to a different char value
in the other column.
Thanks
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Javier

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