Help with database column

Question

I have a report with a column that come from table.
This column is a number and I need change the sign if a condition is true.
I try do this in a format trigger and in a trigger in Data Model (right clik mouse on this item Program Unit). But in both cases it say me when compile :
Err 903. A READ-ONLY VARIABLE USED IN OUT OR IN-OUT CONTEXT.
That mind that I cannot use this variable in this point. Also I try to change the Var and use a User Variable and change the value in the moment of read or print with similar results.
Any help wellcome.
Regards Everybody.

Answer 1

Why do you not use a database function which will have your businesslogic and will return the changes value.
Create function business1 (p_val in number) return number is
begin
<your logic here>
return(l_modified_value);
end;
in your report query just use the function.
select business1(<your_column> as "my alias" from .....
That should work
Marcos