Oracle case函数

update students

            set grade = (

            select grade from

            (

            select id,

            case when current_credits > 90 then 'a'

            when current_credits > 80 then 'b'

            when current_credits > 70 then 'c'

            else 'd' end grade

            from students

            ) a

            where a.id = students.id

            )

            /