[chaley]

If you want to format a composite column (a computed column) then you must do the formatting yourself in the template. I see three ways to do what you want.

1. Use column icons to show an image of stars based on the value. This would be the way to go if you want half-star images.
2. Use something like the following:
   

   program:
   # the variable 'v' contains the computed rating
   	v = 3.5;
   # verify that the value <= 5
   	v = cmp(v, 5, v, v, 5);
   # Check if the value is a fraction
   	halfstar = contains(v, '\.', 'y', '');
   # Make the value into an integer (floor)
   	v = re(v, '\..*', '');
   # Get the string with the right number of stars
   	r = cmp(v, 0, '', '', substr('★★★★★', 0, v));
   # Add the 'half' if needed
   	test(halfstar, strcat(r, '½'), r)

   The value 3.5 produces ★★★½
3. Use a custom formatter function to compute a string containing whatever you want.