> "Computed columns are based on a expression. Column values are are
> computed each time the table is accessed."

I'm not understanding why not use count in a computed column.

So, if I make a "select id_course from course", the columns computed
of the table course will be computed?

As far as I don't mention the computed column in my querys, the
computed column will be computed?

If I make "insert into course (id_course, description_course) values
(1, 'Espanish')", the computed column will be computed?

> So I still keep insisting: What do you need it for?

I have several querys that I need a subquery that return only one
value. So I want to put this subqueries as a computed column in my
table. Then, I avoid use the same codes in many querys.